There are several places where you can use String.Format indirectly: The secret is to look for the overload with the signature string format, params object[] args, e.g.:

Console.WriteLine(String.Format("{0} - {1}", name, value));

Can be replaced with shorter version:

Console.WriteLine("{0} - {1}", name, value);

There are other methods which also use String.Formate.g.:

Debug.WriteLine(); // and Print()
StringBuilder.AppendFormat();

NumberFormatInfo can be used for formatting both integer and float numbers.

// invariantResult is "1,234,567.89"
var invarianResult = string.Format(CultureInfo.InvariantCulture, "{0:#,###,##}", 1234567.89);

// NumberFormatInfo is one of classes that implement IFormatProvider
var customProvider = new NumberFormatInfo
{
    NumberDecimalSeparator = "_NS_", // will be used instead of ','
    NumberGroupSeparator = "_GS_", // will be used instead of '.'
};

// customResult is "1_GS_234_GS_567_NS_89"
var customResult = string.Format(customProvider, "{0:#,###.##}", 1234567.89);

public class CustomFormat : IFormatProvider, ICustomFormatter
{
    public string Format(string format, object arg, IFormatProvider formatProvider)
    {
        if (!this.Equals(formatProvider))
        {
            return null;
        }

        if (format == "Reverse")
        {
            return String.Join("", arg.ToString().Reverse());
        }

        return arg.ToString();
    }

    public object GetFormat(Type formatType)
    {
        return formatType==typeof(ICustomFormatter) ? this:null;
    }
}

Usage:

String.Format(new CustomFormat(), "-> {0:Reverse} <-", "Hello World");

Output:

-> dlroW olleH <-

The second value in the curly braces dictates the length of the replacement string. By adjusting the second value to be positive or negative, the alignment of the string can be changed.

string.Format("LEFT:  string: ->{0,-5}<- int: ->{1,-5}<-", "abc", 123);
string.Format("RIGHT: string: ->{0,5}<- int: ->{1,5}<-", "abc", 123);

Output:

LEFT:  string: ->abc  <- int: ->123  <-
RIGHT: string: ->  abc<- int: ->  123<-

// Integral types as hex
string.Format("Hexadecimal: byte2: {0:x2}; byte4: {0:X4}; char: {1:x2}", 123, (int)'A');

// Integers with thousand separators
string.Format("Integer, thousand sep.: {0:#,#}; fixed length: >{0,10:#,#}<", 1234567);

// Integer with leading zeroes
string.Format("Integer, leading zeroes: {0:00}; ", 1);

// Decimals
string.Format("Decimal, fixed precision: {0:0.000}; as percents: {0:0.00%}", 0.12);

Output:

Hexadecimal: byte2: 7b; byte4: 007B; char: 41
Integer, thousand sep.: 1,234,567; fixed length: > 1,234,567<
Integer, leading zeroes: 01; 
Decimal, fixed precision: 0.120; as percents: 12.00%

The "c" (or currency) format specifier converts a number to a string that represents a currency amount.

string.Format("{0:c}", 112.236677) // $112.23 - defaults to system

Precision

Default is 2. Use c1, c2, c3 and so on to control precision.

string.Format("{0:C1}", 112.236677) //$112.2
string.Format("{0:C3}", 112.236677) //$112.237
string.Format("{0:C4}", 112.236677) //$112.2367
string.Format("{0:C9}", 112.236677) //$112.236677000

Currency Symbol

1. Pass CultureInfo instance to use custom culture symbol.

string.Format(new CultureInfo("en-US"), "{0:c}", 112.236677); //$112.24
string.Format(new CultureInfo("de-DE"), "{0:c}", 112.236677); //112,24 €
string.Format(new CultureInfo("hi-IN"), "{0:c}", 112.236677); //₹ 112.24

2. Use any string as currency symbol. Use NumberFormatInfo as to customize currency symbol.

NumberFormatInfo nfi = new CultureInfo( "en-US", false ).NumberFormat;
nfi = (NumberFormatInfo) nfi.Clone();
nfi.CurrencySymbol = "?";
string.Format(nfi, "{0:C}", 112.236677); //?112.24
nfi.CurrencySymbol = "?%^&";
string.Format(nfi, "{0:C}", 112.236677); //?%^&112.24

Position of Currency Symbol

Use CurrencyPositivePattern for positive values and CurrencyNegativePattern for negative values.

NumberFormatInfo nfi = new CultureInfo( "en-US", false ).NumberFormat;        
nfi.CurrencyPositivePattern = 0;
string.Format(nfi, "{0:C}", 112.236677); //$112.24 - default
nfi.CurrencyPositivePattern = 1;
string.Format(nfi, "{0:C}", 112.236677); //112.24$
nfi.CurrencyPositivePattern = 2;
string.Format(nfi, "{0:C}", 112.236677); //$ 112.24
nfi.CurrencyPositivePattern = 3; 
string.Format(nfi, "{0:C}", 112.236677); //112.24 $

Negative pattern usage is the same as positive pattern. A lot more use cases please refer to original link.

Custom Decimal Separator

NumberFormatInfo nfi = new CultureInfo( "en-US", false ).NumberFormat;        
nfi.CurrencyPositivePattern = 0;
nfi.CurrencyDecimalSeparator = "..";
string.Format(nfi, "{0:C}", 112.236677); //$112..24

string outsidetext = "I am outside of bracket";
string.Format("{{I am in brackets!}} {0}", outsidetext);

//Outputs "{I am in brackets!} I am outside of bracket"

DateTime date = new DateTime(2016, 07, 06, 18, 30, 14);
// Format: year, month, day hours, minutes, seconds

Console.Write(String.Format("{0:dd}",date)); 

//Format by Culture info
String.Format(new System.Globalization.CultureInfo("mn-MN"),"{0:dddd}",date);

Console.Write($"{date:ddd}");

output :

06
Лхагва
06

The ToString() method is present on all reference object types. This is due to all reference types being derived from Object which has the ToString() method on it. The ToString() method on the object base class returns the type name. The fragment below will print out "User" to the console.

public class User
{
    public string Name { get; set; }
    public int Id { get; set; }
}

...

var user = new User {Name = "User1", Id = 5};
Console.WriteLine(user.ToString());

However, the class User can also override ToString() in order to alter the string it returns. The code fragment below prints out "Id: 5, Name: User1" to the console.

public class User
{
    public string Name { get; set; }
    public int Id { get; set; }
    public override ToString()
    {
        return string.Format("Id: {0}, Name: {1}", Id, Name);
    }
}

...

var user = new User {Name = "User1", Id = 5};
Console.WriteLine(user.ToString());

While the String.Format() method is certainly useful in formatting data as strings, it may often be a bit overkill, especially when dealing with a single object as seen below :

String.Format("{0:C}", money);  // yields "$42.00"

An easier approach might be to simply use the ToString() method available on all objects within C#. It supports all of the same standard and custom formatting strings, but doesn't require the necessary parameter mapping as there will only be a single argument :

money.ToString("C");  // yields "$42.00"

Caveats & Formatting Restrictions

While this approach may be simpler in some scenarios, the ToString() approach is limited with regards to adding left or right padding like you might do within the String.Format() method :

String.Format("{0,10:C}", money);  // yields "    $42.00"

In order to accomplish this same behavior with the ToString() method, you would need to use another method like PadLeft() or PadRight() respectively :

money.ToString("C").PadLeft(10);  // yields "    $42.00"