filter for printing!

[bj333]

From last 2 weeks i am taking photography class, today i hv printed some of negaives, made some test stripes but i can not figure out which is best exposure on same exposure setting from same film negatives i can get different kind of image. (when i put all my negatives to test on same print paper after tring lots of test stripe for different negatives)

Today my instructor has introduce regarding filter, she was showing different kind of filter to us by thier number. What does this filter actually do when we print? Like she was saying regarding cotrast but i didn;t got chance to play around with it, may be i am gonna try ti tommoro, Does this helps (filter) me to get good picture.?
What is burning?
Regards i know this sounds boring to answer back but please help me to understand!
Cheers!