Welcome.
This topic does come up fairly often, so you might want to do a search if you haven't already.
People are going to have a lot of different opinions about what ammo they use in their snub revolvers for practice and carry.
For practice I like to use some form of 130gr full-metal jacket (FMJ). Recoil isn't too bad in a lightweight snub. 158gr lead round nose (LRN) or semiwadcutter (SWC) are other options.
The general consensus on the best defensive load is the Speer 135gr Short-Barrel Gold Dot JHP +P. It's what I carry in my 642-1.
Alternatively, the 158gr lead hollowpoint (LHP), or lead semiwadcutter hollowpoint (LSWCHP) as it's often called, in +P, often referred to as the FBI load, is another good choice.
However, both of those can have some pretty stiff recoil, especially in a lightweight snub like the 642, so probably not the best choice for a new shooter.
148gr target wadcutters are a good option for both self defense and range use, especially if you need a lighter-recoiling load. You do need to test the ammo at the range to make sure the bullets don't tumble, which can happen from such a short barrel. You can tell if it leaves tears in your targets instead of nice, clean, round holes.
Unfortunately, with the ammo availability problems we're having, it can be very difficult to find good ammo, or any ammo. You may just have to settle for whatever you can get and do the best you can with it. You can try using AmmoSeek to look for online sources of ammo.
Best Ammo for Finding Ammunition 2020 - Guns Mags Reloading | AmmoSeek.com
Also, if you're new to shooting, I'd highly recommend you get some training. Shooting ranges often have courses for beginners and sometimes courses for self defense and concealed carry.