Bike manuals are pretty generic, and not always very helpful, containing only safety and very basic info. Also, 15 speed bikes have not been produced for some time, so it would be difficult to obtain a manual.specifically for a 15 speed. Here's a link to a manual that may help: https://www.huffybikes.com/content/pdf/ownersmanuals/7f448214-b108-4c48-93eb-972b6c9e4a17.pdf If you need to know how to use the gears just Google "how to shift bike gears" and check out both written and video guides. Finally, for maintenance check Repair Help
usually at the bottom under the cranking for the pedals, tip bike upside down and you should see a number pattern in the paint were it was stamped. there are other places but this id for the recovery of a bike that has been stolen and the number has been grinded off. also the paint is code.
Lots of things on a bike move in circles. If you mean it moves when you pedal but does not "catch," so the bike does not move forward then that is a problem with the rear gear cluster. You need to have a mechanic look at it. If that's not what you mean you need to get help in providing a more clear explanation. I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881
contact the manufacturer on the net
see if there is a pdf down load on a page relating to the make and model
ask your local agent for that brand of bike to see if one is available