The choice of weight depends on your level and the muscles being worked.
There's a correct weight for every level. You should be feeling it when you finish your reps.
Your lower-body muscles (thighs, buttocks, etc.) are larger than your upper-body muscles (shoulders, biceps, etc.)
You should therefore use heavier weights for squats and lunges (from 2kg) and a lighter load for your smaller upper-body muscles (1kg).

Don't know which exercise to start with, or how to get your posture right?
Take a look at the poster below:
https://contents.mediadecathlon.com/s839587/k$f50a938fc6d427f41f23dccaee7056d6/fiche%20dumbells%20a4.pdf

(By copying/pasting this address in your web browser)
With certified coaches, our design team has developed a dozen free exercises available in this poster that you can easily print or download on your phone!

It's important that you always start by fully warming up your body using lighter weights so that your body will be ready for your workout and won't get injured.
Beginners should start with light weights (1kg) while they get to grips with the technique of the movements.
Once you're familiar with the moves, you can gradually increase your weight (by 500g each time) every other session.

Vary your training for increased effectiveness
Experiment with the amplitude, load and speed of your movements!