To be a sponsor one must be a fully initiated Catholic who is able to receive the Eucharist. In other words, a person must be baptized, had first communion and been confirmed. If the person is married, they must be married in the Church. If not married they must be living life as a single Catholic should. A sponsor should also a better than nominal knowledge of the faith.
A sponsor is someone who walks with a candidate during their journey toward confirmation. They give the candidate insight into the faith, pray with them and for them.