Dear Babyhim,
Then have to see which kind of stroller (baby car) you have. If you have the one we called "travel system", that is included "an infant car sear carrier" and the "stroller".. you can use it from birth, certainly!!!
If you have the one we called "deluxry stroller" which you can recline the back to 45 degree, it is good for the baby who is older than 6 months old, as the back is soft.. if your baby can not sit.. it will not provide a good back support for your baby.
If you have the one we called "100% recline", which you can recline it as a bed for your infant. with the hard back. With good support. but then, they normally don't have the 5 hassel security.. it means your baby may fall off if attended.
If you have the one we called "umbrella stroller".. which you can pack it up and less than 7lbs.. those.. it is only good for kids who can walk.. also.. it is not secure, the less protection.
the web site below just a guideline for you to have a look...
with many kinds of stroller here, it is a pretty popular web site here in USA