nissian altima 2003
how does the shifting work ? is it a manual and an automatic?
It's called CVT (Continuously variable transmission) They use a metal belt to drive transmission pulleys via solenoid valves. Nissan had a lot of issues with these transmissions.
Your car has an 4 speed automatic or a 5 speed manumatic transmission. Can't say which one you have. Based on your question you may have the 5 speed.