The weight you use depends on your skill level and the muscles being worked.
There's a right weight for every skill level. You should be able to complete your reps but be tired at the end.
Lower body muscles (thighs, glutes, etc.) are larger than upper body muscles (shoulders, biceps, etc.)
This means you should choose heavier weights for squats and lunges (2 kg and up) and a lighter load for 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 (1 kg) until they learn the right technique.
Once you have the basics down, you can gradually increase the weight (by 500 g) every other workout.

Vary your training for better results
Change up your range of motion, weight, and speed!