The specifics will depend on your parish, but the main thing is be there, live your faith, be an example.
The main job of a sponsor is to be there and encourage them. You should be there to help answer questions, or point them in the right direction to someone who can answer the question. You are the representative of the community. You should help welcome them, help them find their place in the community. Eventually you will also be asked to testify on behalf of your person that they really have experienced a conversion, that they are ready to be Catholic.
You will have to ask the RCIA director for more specifics. Often you will be asked to attend classes so you know what they are learning and can support them. There will be a number of Rites that you will be asked to participate it.