Installing a second OS on my PC?

So I was parying attention to my computers startup and it said for options press escape, so I did. I was pleased to find that that was the menu to chose the OS I am going to boot up. I want to know what OS would be good to install, and it’s features. My current is Windoes 7 and I was considering XP but decided not to. What should I install, and do you have any advice on how to do it? I know it involves windows partitioner but that’s pretty much it. I would like an OS that is free and that I could download.

Also, do you know where I could get adobe photoshop for free? I don’t really have the patience for a torrent, but maybe a survey site or something?