1. Go to File --> Settings (e.g. Ctrl+Alt+S ).

2. In the left-hand pane, select Plugins.

3.On the Plugins window, click "Install JetBrains plugin" or the "Browse repositories button".

1. Go to File --> Settings (e.g. Ctrl+Alt+S ).

2. In the left-hand pane, select Plugins.

3. On the Plugins window, click "Install plugin from disk button".

4. Select the desired plugin from your local machine. 

   Click Apply button of the Settings/Preferences dialog.

Or you can directly add pugins from the other venders by directly searching the repositories.

1. Go to "Browse Repositories"

2. Select the category (on the top of the window) that you need to search(or just search by the name if you know it).

3. Install it.