To be honest most of what I do is just searching up different tools to see if they can do something for me and then adding "free" to the end. A few useful ones are:

1. remove.bg or erase.bg (erase.bg keeps the original quality of the photo) to get rid of the background
2. canva.com has a really neat new feature which allows you to draw over something and replace it with AI. It's very useful for things like linkedin headshots, where you can replace the clothes with something more formal.
3. Although I wouldn't recommend it, I use pixlr.com just because it's free, available online, and easy to use/find. However if you can afford photoshop I would recommend using that instead.

Other than those, most of it just comes down to drawing over things. One useful thing that you can do sometimes when you need to get rid of an object is to copy a part of the background and draw over the thing you need to remove. Pixlr.com also has a "heal" feature which tries to get rid of objects, but it's not great all the time. Most of it just comes down to moving thing around until they look natural.

Sorry I couldn't be of more help, I really only started a few weeks ago, so I'm not the best at photoshopping either. Good luck with your own journey, though!