See sorting in the vim manual for the canonical explanation
Highlight the text to sort, and the type:
:sort
If you don't highlight text or specify a range, the whole buffer is sorted.
:sort!
:sort i
Sort by the first number to appear on each line:
:sort n
:sort u
(u stands for unique)
To get a reverse case-insensitive sort with duplicates removed:
:sort! iu
:[range]sor[t][!] [b][f][i][n][o][r][u][x] [/{pattern}/]
Note: Options [n][f][x][o][b] are mutually exclusive.