Took in a male feral cat. How do we get him to use the litter box and how do we introduce him to our

We just took in a male feral cat. He hung around a mechanic shop. Apparently he lived in back with a colony of some other cats and was seen sometime with one other female cat by the shop. They would feed him sometimes and he was friendly toward them. We have taken him home put him in his own room. Got him a separate litter box and provided him with food and water. He was eating so fast it didn't seem like he was chewing. Tried to give him dry food but he didnt seem to be chewing it and sort if choked so we we gave him wet then mixed in a little dry. He didn't use the litter box he pooped under a desk in the room. Then he peed on the ledge of the window. We are getting him neutered Monday. Any suggestions on how to get him to use the litter box? And what are the best steps to take to introduce him to our other cat Cali a girl.

I'm not very experienced with cats but I will try and help. I not only am current going through my first cat experience, she is feral and pregnant. You have your work cut out for you. Put him in a room by himself with a litter box, food and water and let him get use to it. You may want to interact with him with a toy and talking softly on a daily basics. He doesn't want to use the litter box, he would rather go outside, make sure you are using unsented litter. you may even wanna put a few leaves in the box also.
Good luck!

Can you pick him up and put him in the littler box and let him walk out on his own? If not I would put the littler box under the desk where he pooped and take some used litter from your other litter box and put some in his to make it smell like where he is supposed to go. I think the best way to introduce is during feeding time. Maybe put them in a large common room within eye shot of each other while someone is petting both. They will associate something good with each other. There will always be spats at first.

Since he is used to going outside, you can mix a bit of dirt/soil in with the litter or you can get a product called Litter Attract by Dr. Elsey's.  Most pet stores carry this product.  You can start by just using the Litter Attract or mixing it in with your current litter.  When I brought a feral/stray into my home last year, I had the same problem.  He pooped in a corner and peed on the floor.  I got 2 litter boxes and mixed one with soil and litter and the other I just used the Litter Attract.  Within 2 days, he was strictly using the Litter Attract box and not one more single accident. 

Thank you for taking in his boy and also for getting him neutered!  He now has a loving home. 

When you are ready to introduce him to your other cat, read this article  http://www.thecatsite.com/a/introducing-cats-to-cats  It has great tips.  I would plan on keeping them separated for awhile to allow the feral to calm down after the neuter as well as letting the hormones dissipate for a few weeks.  The cat to cat introductions work really well.  They just have to be followed and not rushed.  I learned the hard way and rushed a few steps.  I had to go back and redo the entire process.  It does work.  There are also products such as feliway adapters, feliway spray, flower essences and calming treats which can all help the process. 

We are are to help so ask questions as needed.

As ShadowRescue said, Litter Attract works well, as do either dirt or leaves on top of the litter.  He probably doesn't know what clay litter is for.

Also, make sure to buy a good enzyme cleaner to clean up the pee.  If he still smells the scent of it, he will pee there again.  The enzyme cleaner gets rid of that smell.