Help with WP Translation

Hi. I’m trying to change a string like ‘Ask Question’ to ‘Post’.

I’ve read that I have to use WP translation but I just couldn’t understand how to do it. There’s a post that says ‘wplang’ in wpconfig, but when I go there, there is none set.

Can you provide a definitive noob guide on how to do this? I’ve also tried poedit to make a new translation but I don’t know how to make my uploaded .mo .po file the default file.

I’m out of my wits here.. Can someone help.

Thanks.