When using grep from VIM, how to jump to results?

When you press ENTER, you should be looking at line 3 of file1.txt. To jump to the next match, execute :cn; to jump to the previous match, execute :cp. Executing :copen will open a window containing the list of matches. Move the cursor to the desired match and press ENTER to jump to that match.

For more on using :grep, see

:help grep
:help quickfix.txt

Typing :cn and :cp to move forward and backward in the quickfix list can be awkward, so I use these mappings:

nmap <silent> <C-N> :cn<CR>zv
nmap <silent> <C-P> :cp<CR>zv

Also, the :grep command is not a plugin; it's part of Vim.