As for your first question, do you mean can you take a SSD from laptop and put it into a desktop or do you mean do desktops also use SSDs? SSDs will help you load things faster, I used put my most played games on it and my OS on it while I put the things I don't use/play most on the HDD. You can get this one if you want to go cheaper.
http://pcpartpicker.com/part/samsung-internal-hard-drive-mz7te250bw