I started using my mom's sewing machine for the first time a Silvercrest SNM 33 B1 sewing machine, but the thread on it keeps snapping.
Why does this happen? Is it my needle's fault or are the threads bad?
Many sewing machine issues can be resolved by simply removing the thread and re-threading it. Your machine's manual should have a diagram showing how to insert the thread. Even if you're sure you already know how to thread the machine, find that diagram and follow it step by step. You may find that you've been missing a step, or putting the thread in the wrong place.
Even if you don't figure out what the issue was, sometimes re-threading will solve it anyway. The thread may have been getting snagged or dragging somewhere along its path, and by re-threading it, you may fix that issue.
As you feed the thread, watch for any places that seem rough, or slots that seem tight. Manually pull the thread back and forth through each slot and around each turn, checking to see if it snags or tugs anywhere. It should pull smoothly through/around each point.
Here's a troubleshooting guide for the Silvercrest SNM 33 B1 machine. It basically says what I mentioned above, but it has diagrams for how to re-thread.
Make sure the bobbin is inserted in the correct orientation, as you can see in this snipped from the troubleshooting guide. My machine (which is a different brand) will work when the bobbin is in the wrong way, but the thread snags and snarls much more frequently.
Also check to make sure your needle is not bent, blunt, or damaged. If you can't tell, swap in a fresh needle just to be sure.
It could also be the threads fault. I've had similar problems very recently.
I sewed some seams with new synthetic thread and never had a problem. Then I switched colors and grabbed a random spool from my moms stash and the thread snapped several times. It was a spool of cotton thread that was at least 20 years old and the thread was slightly thicker (I had more problems getting it through the needle). I still don't know where exactly the thread snags, but switching between both colors several times confirmed that only the old cotton thread had this problem.
Another possibility is that the bobbin isn't inserted correctly. I had that problem when I just started sewing on a machine and didn't notice that the bobbin of my machine jams sometimes. Most of the time it pulled long loops (as seen here), but sometimes the upper thread snagged somewhere in the bobbin compartment and snapped.