The term "sponsor" has a number of different meanings. I can refer to:
Legislators often sponsor a bill when they decide that a change is necessary. It is common for multiple legislators to co-sponsor a bill. This can give the bill more strength and increase its chances of passing. However, to become law, a bill still needs to be approved by the necessary government bodies, such as Congress.
In terms of immigration, companies are often sponsors for immigrants whom they want to bring to the U.S. for business reasons.