there are two steps to RSUs
1) step one is when the restriction comes off. The income is taxable to you at that point which is why some of the shares are sold (to pay the taxes). Everything is already in your W-2 so nothing special to do when reporting your tax return.
2) but sounds like you immediately turned around and sold those vested shares. There is also a small gain or a small loss when this occurs since it is unlikely you sold the shares at the very same price they vested. This is why you received a 1099-B, which must be reported by you on your tax return. Be sure you get the cost basis correct - which is the same stock price that the RSUs converted at.
Make sense?
