My car won’t move in drive it just revs up like it’s in neutral-is it the transmission?
If you checked the transmission fluid level and it is full and still won’t go into any gear, then yes the transmission is faulty. It may have lost the front pump or an input shaft which can cause it not to function. You will need to replace the transmission. If you had something electrical it would still go into gear but would be in a limp mode. Since it does not go into any gear the transmission is the problem
It’s an automatic but when I drive it manually starting from second gear then it drives
Does it go into reverse and only lost first gear?
It goes in reverse fine and once I’m driving I can put it into drive at highway speeds and it works.
This sounds like you lost only first gear. You may have lost a part of the transmission. What would need to be done in your situation is to have a transmission technician inspect the transmission and see if it is a problem in the valve body or a hard problem which would require the trans to be opened up. More than likely the problem is going to be a mechanical issue with the first gear clutch/brake. It is possible that there may be a leak in the valve body causing a loss of first gear, but not likely.
Is that as expensive as replacing the whole transmission?
Sometimes it’s almost as expensive. Depending on the repair facility it can cost anywhere from $500 - $700 to replace a valve body. If your vehicle has a lot of miles then it’s not really worth spending that kind of money on a transmission that is probably not going to last a lot longer. It might be better finding a good used transmission for less.