How to jump to the start or the end of visual selection in Vim?

The easiest way to "surround a visually selected area with parentheses" is:

change the visually selected area to () and Put it back in the middle: c()<ESC>P

I suggest defining in the .vimrc file a new visual-mode command (e.g., \q) with that:

:vmap \q c()<ESC>P

This approach also works with visual rectangular areas (<C-V>): it puts ( and ) around each block-line.

There are two relevant built-in marks holding the positions of the first and last characters of the last visual selection in the current buffer. In order to move the cursor to these marks, use the commands `< and `>, respectively (see :help `> and :help `<).

While you are in Visual Selection click o. It will change position of cursor to other end of selection. Then O to jump back.