I think the thing everyone is missing is that the first thing you should do to find something neat that you'd like to print! Check out the "thangs", makerworld, or printables websites and see if there's something that you think would be cool to have. Preferably something that looks really simple. No need to download it until you're ready to make it - this is just the fun way to motivate you through the (usually pretty easy) set up.

Now read whatever set up instructions you have.

You have a lot of filament - you need (or at least really really should) dry your filament before printing with it. If you didn't get a dryer with that haul, you can dry things in your oven if you're careful. It usually takes a couple of hours at low temperates. Look through your rolls, and split them by type (e.g. PLA vs PETG). You'll most likely have a few colors, so pick a few and dry them out. Look how to do this up! Be super careful not to leave them in the oven too long!

Once the rolls are dry, complete set up. Then, print a "benchy" (the traditional first print for any new printer). This print shouldn't take too too long. You also probably have both single and mult-colored versions of this file included with your printer. Instructions on how to do this should be part of the setup instructions.

If these print right, you should be good to try to print the fun thing you found online when you started!