In insert mode, line indentation can be manually adjusted with ⌃T to indent or ⌃D to unindent.

In normal mode, line indentation can be manually adjusted with > to indent or < to unindent.

Examples:

Indent two shiftwidths over an absolute line range:

:10,90>>

Indentation with one shift width over a relative line range (unindent the previous 10 lines by 1 shift width:

<10k

Unindent an entire buffer:

<gg=G

Indent a text object (an inner paragraph in this case):

>ip