craftgrrl | question from a sewing newb

Hi!

I am very new at sewing and don't want to ruin my machine, so I thought that I would ask you guys for a bit of knowledge and advice.
I have a Singer 57815c and when I began sewing it went smoothly. However, soon the stitch on the top looked fine, but underneath it was a rat's nest with the thread bunching and catching. (Deception!!) My sister told me to adjust the tension. I did this and it was again fine for a while. However, it soon began to bunch underneath again. Repeat....repeat...etc. Somewhere in the midst of all of this I broke a needle and and bit of plastic broke off of the piece that holds my bobbin.

Do I need to replace this piece? Bring it in to be serviced? ( I am very poor right now, so I can only do this as a last resort) And do you have any other advice for using my machine or adjusting tension?

Thanks so much! I have been watching this site and am excited to hear your expert advice!!!!

~Redd