Hi Jinnie -
The Roma Pass website is your best resource for using the card:
https://www.romapass.it
The FAQ section is your go-to for most questions:
https://www.romapass.it/en/FAQ/
Is it still the case if I have the 2 days Roma pass that i can get in
one of the site for free?
Well, it's not exactly 'free' as you pay for the card but yes, entry to a single (1) attraction on the website's museums list is covered under the 48-hour card. Be aware, though, that if your choice is the Colosseum you are still required to make an advance, timed-entry reservation. Same for Galleria Borghese. See the #7 "Reservations" section of the FAQ page for how to do that. See this page of the Parco Archeologico del Colosseo website for info on free-entry tickets for children under the age of 17; the link on the FAQ page for children's Colosseum' tickets is no longer operational.
https://colosseo.it/en/2023/04/free-tickets/