Vim has quite a few features for automatic text completion. The most basic is keyword completion - 1) open a file, 2) write first few characters of any word you see in the file, 3) hit CTRL+N to automatically complete the word. Simple, easy to use and very useful.

To make this feature more intuitive, consider mapping CTRL+Space to CTRL+N:

1 inoremap <C-Space> <C-n>
2 inoremap <C-S-Space> <C-p>