comparing - present tense "i am comparing my notes to the one on the board." compared- past tense "i have compared my notes to the one on the board."

Learn something called "non-finite verb" (aka "verbal").

'Comparing' is a noun, a verbal one from the verb 'to compare' "Comparing the texture of the 2 substances led him to conclude different results." 'compared' is the particip of the verb 'to compare' ( e.g is,was compared) or the verb in its past tense. "She compared John to her previous boyfriend and found no resemblance." P.S 'comparing' could be also part of the present continuous tense formation as Christine noted.