Have you got the check engine light on? Usually, when you only have one forward gear and reverse, the transmission is in safe mode because it has a problem to permit you to get off the road and get the problem fixed. If you can get to an auto parts store, ask them for a free OBDII scan to see what codes come up.
The code will tell you what is wrong in general terms. With the code it narrows down fixing the problem. We can then help you decipher the codes and see what repair is necessary.