A prefix is placed at the beginning of a word to modify or change its meaning. This is a list of the most common prefixes in English, together with their basic meaning and some examples. You can find more detail or precision for each prefix in any good dictionary.
A prefix goes at the beginning of a word. A suffix goes at the end of a word.
The origins of words are extremely complicated. You should use this list as a guide only, to help you understand possible meanings. But be very careful, because often what appears to be a prefix is not a prefix at all. Note also that this list does not include elements like "auto-" or " bio-", because these are "combining forms", not prefixes.