stiches problem HELP

ok i am not a good sew person but i do like the idea of sewing..does
that make sense? haha
i have a sewing machine my aunt gave me with everything i need to sew
but when i begin to sew i stitch a few times and i think all is ok and
then BAM the stitches arent sewing on the fabric or they are bulking up
and are a big bundle of th reads and i have to go back and rip it
apart...i cant seem to get my sewing machine to just sew a straight
simple stictch..i seem to have this problem often..i think maybe its the
way im threading the needle or maybe the tension but i dont know what it
should be on..im an idiot to this sort of stuff..i have so much material
and threads and embellishmetns my aunt gave me and im wasting it by it
sitting there..
any suggestions why my thread bundles or doesnt sew at all on the
material?
fustrated...cathy