You should first look into one of the boxes of siding and take out the instructions. But, the key thing to remember is, think backwards work forwards.
What I mean by that for example is you need to know where you want the siding to end to be able to install the starter. You want to install the corner post first, then the J channel and starter.
Hint* siding is not nailed, it is hung. It should be hung level so, find the lowest part of the garage and work your numbers from there. Depending on the product you are using, will depend on the formular to use.
Examples, If you are using double 4" vinyl siding, with a true 4" to the weather, you would work in 8" incriments.
If your double 4" is truly double 3 3/4", you would work with 7 1/2" incriments and so on with double 5", 6"...
the amount you overlap the joints usually is about 3/4". but you need to follow the manufactures recomendations in order not void your warranty.
After you lock your first piece of siding into the starter, you should hold that piece up snug and using aluminum plain shank nails, (NOT ROOFING NAILS), nail in the middle of the nailing slot and leave the nail head out for the siding to slide on. After that, you should be able to lock the next pannel in and let it hang befre nailing. All you are going to have to do is measure your butts for the right "to the weather".
I hope this helps you get a broader scope of what you need to do for a well hung job.
As I mentioned before, be sure to read and follow the instructions in the box so you don't void your warranty!