augroup MyGroup
" Clear the autocmds of the current group to prevent them from piling
" up each time you reload your vimrc.
autocmd!
" These autocmds are fired after the filetype of a buffer is defined to
" 'foo'. Don't forget to use 'setlocal' (for options) and '<buffer>'
" (for mappings) to prevent your settings to leak in other buffers with
" a different filetype.
autocmd FileType foo setlocal bar=baz
autocmd FileType foo nnoremap <buffer> <key> :command<CR>
" This autocmd calls 'MyFunction()' everytime Vim tries to create/edit
" a buffer tied to a file in /'path/to/project/**/'.
autocmd BufNew,BufEnter /path/to/project/**/* call MyFunction()
augroup END
See :help autocommand
.