If you have time and want to learn autographs, this site is very helpful.
If you want to buy a few things and don't want to waste money on something inauthentic, purchasing third party authenticated items is a good solution. There are some that do their best to get it right and some print certs with the intent to sell forgeries.
JSA, PSA, Beckett, and SGC all try to get third party authentication right.
If you have autographs that you don't know if they are authentic, there are people willing to help with items posted to the Authenticity Opinion forum.
I think the comments above are great if you have items that you're looking to sell.