syn spell toplevel
set spell spelllang=en_us
(or whatever language you speaks)
Then, mispelled words will be underlined in red in Gvim, and highlighted in Vim.
Some useful commands:
- ]s move to the next mispelled word
- [s move to the previous mispelled word
- zg add a word to the dictionary
- zug undo the addition of a word to the dictionary
- z= view spelling suggestions for a mispelled word
For more information, type :help spell in Vim/Gvim.