Help would be appreciated… basement bathroom sink vanity vent question

[Broncorado]

Long time reader 1st time poster, I have a question on my current roughed in bathroom in basement. The pipe on the right is 2” and is labeled future lavatory, the pipe on left is 1 1/2” and runs up into the next floor and I believe out the roof. There is no water above this area on the main level. My question is for the sink drain I’m I just tying into the pipe on the right or am I tying the pipe on the right into the pipe on the left and then tying in the sink drain there? Sorry if the question is worded poorly or if this is confusing. Thank