Put the camera in a changing bag or go into a light-proof room. You'll also need an empty black (light tight) plastic film container. Then press the rewind button at the base of the camera and pull out the film. Then manually roll up the film starting at the end of the film working your way to the beginning. You need to do it this way because rolling it up the other way will cause you to loose the last few frames as the film is put into the developing machine. Once you've got the film in the canister, put the top back on and you're done.
I would highly recommend that you tape the top of the canister to prevent someone who doesn't know that there's raw film inside, from just opening up the can.
You can now take it to a local lab for developing. If you have to mail your film out, make sure to include highly detailed notes in the processing envelope.
What you should expect is that the film that was visible is going to be completely fogged. The light will have traveled through the sprocket holes and will in essence produce shadows on the underlying film. Additionally, you'll should expect that every 3rd or 4ty frame to be fogged for about 1/3 of the roll.
If you want to continue shooting film, but want to avoid this problem, I highly suggest getting an EOS-1 SLR. They have various models 1, 1v, 1n. They're designed with a piece of plastic that covers the film, so when you accidentally open the roll, you only expose the last frame. I had this happen to me during a wedding reception and was very grateful that Canon designed the camera so well. Plus the EOS series of cameras will tell you if the film was loaded properly and will automatically rewind at frame 24 or 36. You'll have fewer problems with an EOS-1 than you AE-1. You're lenses can be adapted to fit and work with the EF mount. But in all honesty, getting an AF SLR vs your MF one, is a better choice because the lenses work without adapters or issues with the current DSLRs from Canon.