got a git merge issue after git pull

It seems you are now in vi or vim.

press i, then input your merge message.

Then esc, and :wq

You are probably using VI as your editor. You can do two things: press 'i', or 'a', and you will be entering type mode, which can be exited using the ESC key, and then press ':wq', or 'ZZ', which will save the file.

An alternative is probably to use the -m switch on the command line, which will allow you to skip this screen, and supply a message immediately (-m "My message here")