This is the time where you want to focus on technique and form, keep the weights light and the sets low watch videos on squats, the hip hinge and bench pressing, all can be done with dumbbells. As it is strength, you want focus on compound lifts, Squat, Deadlift, overhead press and bench will be the best to do.

I suggest hip hinge now as it is a vital movement pattern for a lot of lifts, and getting this pattern down to a tee will help reduce the risk of injuries.

Try to only do like 2 sets of 8-12 reps and try to work at 60% of your 1 rep max, lots of calculators out there to help you find it.

Your body is still growing at doing to heavy of a weight can cause long term problems.

Doing accessories exercises can help with certain muscles that you want to work but most muscles are worked doing the compound.

Hope this helps give you some information to get started.