Shopify has some great content on this. If you haven't seen this, check this out:
https://www.shopify.ca/guides/dropshipping
In terms of selecting products to sell you can go to various websites like AliExpress, DHGate, GearBest, etc. and search for the best-selling products and start that way. The key here is to avoid selecting products in saturated niches where you will have a lot of competition.
I'm actually developing an AliExpress product research tool to help simplify and speed up the product research process. I currently have an early access program setup. If you're interested in learning more and receiving a 25% lifetime discount for the tool, check out:
https://threadanalytics.com