Online buying and selling: do you have advice for me?

OK, so I’m finally getting around to try and clean up my parents’ stuff that’s been stored and taking up too much space in my garage, my extra bedroom, even my living room…
A lot of stuff will be donated or given away, of course. But there are things that may be of some value in the used merchandise marketplace. I’m thinking maybe Craigslist or eBay, but I’m a newbie at this. I’ve only used Craigslist to give away stuff.
What advice can you give me? Are there other sites that are better suited to my purpose?
Would it be advisable to set up a PayPal account? Is this easy to do and what should I watch out for?