Thread snapping and needle breaking sounds like wrong threading or wrong setup.

All sewing machines needs service now and then. Give the machine some TLC, oil all places, check with the instruction manual if you have it. There are holes to be oiled, lids to be lifted, sometimes loosening of a screw or two is needed. All models and makes are different this way. In general: move all joints and moving parts that touch, it is all about reducing friction.

Check for any threads and lint around the bobbin case and feed dogs (unscrew the needle plate if necessary). It's surprising what can gather there over time.

Double check that threading is done correctly on both under thread and over thread. Some models are very particular, the bobbin has to go in the right way (the way it is wound).

Then check needle, sometimes low quality needles make machines act up, if possible use Schmetz or Orgran during truble shooting.

Check that the needle is put in the correct way for your model (flat side either to the right, left or backwards). This should give you an indication of how the needle is threaded, usually straight on when the flat side of the needle is in the back (facing away from you). Make sure the thread doesn't go around the needle, only straight along the shaft through the hole and under the pressure foot and backwards.

Needles needs to be replaced quite often, and make sure they are sharp and not bent. Thicker needle for denim and heavier fabrics, finer for thinner fabrics. Always sharp needle unless you sew jersey or knits.

This might have solved the problem, but if not:

When you have double checked correct insertion of the needle, set the machine to straight stitching. Make sure the needle doesn't hit the needle plate by manually moving the balance wheel. There is most likely a function for moving the needle to the left or to the right, and there is often a mark on the needle plate for correct posistion.

Don't drag the fabric at all when trouble shooting, let the feed dogs do all the work.

You most likely don't have to adjust under thread tension, but double check that upper thread tension mechanism is clean and lint free. Some models have automatic tension (Bernina had it on their 60s models), others have a manual knob with numbers, models differ a bit that way. If upper thread tension is too high the tread will snap, but most often it is wrong threading or setup when adjusting the tension doesn't solve it.

Only bother about this after straight stitching works fine:
Then set the machine to zigzag, check the needle movement manually with your hand turning the balance wheel a few times. The needle should go clear of the needle plate and move within the space it is meant for. There is limit to how wide the zigzag stitch can be set (how far the needle arm swing from right to left when sewing).

Wow! Thank you. That gives me a lot to work on. I have very limited understanding of my machine. I just use it for occasional clothing alterations. I do have a photocopy of the manual, so I can try to refer to it to help me with the adjustments you mentioned.Maybe I will get lucky.