Answer:
It depends on what you're asked. In a question, te gusta means "Do you like...?". You would respond with either "Sí, me gusta ...." or "No, no me gusta ...."
So if someone asked "Te gusta nadar?", you'd respond with "Sí, me gusta nadar." if you do like to swim, or "No, no me gusta nadar." if you don't like to swim.