It is "você gosta de leite" or "tu gostas de leite". The verb gostar has to have "de" (of) after it. Always! =)
OK, except when answering a question or when you don't intend to follow the verb with the description of what the liking refers to. Here's an example of what the exception looks like:
– Você gosta de leite? (Do you like milk?)
– Gosto. (Yes -- we respond with the verb, usually)
– Eu achava que ela não gostava (I thought she didn't)
So if there is a definition of what the liking is about (meaning, if you are going to mention the milk), you need to use the de. Always! =)
Anyway it's useful to learn "Tu" because in some situations it helps. I belong to a French speaking group learning Brazilian Portuguese. When we speak in Portuguese among ourselves to practice the language we use ''Tu'' as we would have used it in French. When we correspond with brazilian friends on the internet we use ''você''. It's more cultural than linguistic.