Bridesmaids and groomsmen are usually invited by the woman, and the man calls them bridesmaids and groomsmen. They all helped at the wedding. The specific situation varies from place to place, but it is basically the same.

There is no need to prepare clothes for them, everyone will dress themselves up.

Usually the bride and groom know each other very well. Classmates, relatives, colleagues, whose?

If you still don't understand, you can ask a married person or a master of ceremonies.