tends to be aspirated - that means you hear a puff of air after the consonant sound. If you say "pin" or "pout" and put your hand an inch or so away from your mouth, you'll feel a puff of air, written in IPA as [pʰ]. Indonesian p is unaspirated (IPA: [p]) - there is no puff of air - so the Indonesian p in pasar or sepuluh is not pronounced with the same amount of aspiration as the English initial p. This makes Indonesian p sound a little like English b, because English does not have unaspirated consonants at the beginning of words. However, the sound is really closer to the sound in words like "spin" or "spout" - if you put your hand back up by your mouth and say those words, you'll notice there isn't so much of a puff of air. So don't pronounce Indonesian p like English b; pronounce it as an unaspirated p - a p without a puff of air - like in sPort or sPill.