How do I combine 2 or 4 photos into 1 image?

That is let's say I have a before and after photo that I want to post to a forum or whatever, but not as separate photos. I want one to the left and one to the right of a single frame.

What's the easiest/quickest workflow for that?

(because the way I'm doing it is awkward and time consuming and almost certainly wrong).

Cheers.

Oh I've tried youtubing this but dont know how to describe it to do so properly


I know this is a very basic (somewhat embarrassing to ask) question but I know that I am doing it the very hard way... so much so that I can't even describe it properly.

Thanks all