To easily save the current file, while keeping it open, use a mapping in your vimrc:
noremap <Leader>s :update<CR>
With the default leader key, just press \s to save any changes to the current file. If the buffer has not been modified since the last save, the file is not written.
On many Windows systems, the file mswin.vim is sourced when Vim starts. In that case, Ctrl-S is mapped to :update, so the above mapping is not necessary (press Ctrl-S to save).
- :help :update command to save file if changed
- :help 'autowrite' option to automatically save file before certain commands