I'm not sure what you mean by that question. If you're asking if they are safe to use than yes they are totally safe(unless you drop it on your toe
) but, it depends on which weight you choose too. I am 15 also and am training with my brother's friend who is 20. He has really helped me and taught me a lot about training. If you want to tone your arms I can suggest many excercises. Always remember though if you work out one muscle such as your bicep you NEED to work out the opposite (Tricep) otherwise you will develop muscle issues and problems. As you said you want to just tone your arms you are going to want to use a weight that you can get maybe 10-12 reps on the first couple sets than go down to 8-6 reps. A good bicep excercise is the isolated bicep curl.
Basically just hold the dumbell, sit on a bench or bed or something and push your elbow against your inner thigh area and place your arm perpendicular to the ground and just bring the dumbbell up only using arm. Also look up windmill curl and other curls. For triceps what really works is tricep dips. To do these you will need two benches sit on one and place legs on other and than lift and dip down using your triceps and extend back up and you will also want to do some forearm excercises I suggest just searching google or another search engine, there are tons of excercises for every arm muscle Good luck!