I believe you want z+c to close the fold. You can read more by typing :help fold in vim. The following is pasted for convenience:
zo Open one fold under the cursor. When a count is given, that many folds deep will be opened. In Visual mode one level of folds is opened for all lines in the selected area.
zc Close one fold under the cursor. When a count is given, that many folds deep are closed. In Visual mode one level of folds is closed for all lines in the selected area. 'foldenable' will be set.
Also, za can be used to toggle the fold open or closed. There is a vim tip on the wiki that describes mapping the key to the spacebar with the following:
nnoremap <silent> <Space> @=(foldlevel('.')?'za':"\<Space>")<CR>