Entry level mechanic positions consists of building bikes out of boxes. If the shop employs mechanics who actually know what they're doing then you'll soon get into basic repairs and you'll be taught more stuff.
You won't be put onto customer bikes immediately, not without supervision and not for anything more than basic anyways. Show a good work ethic, be willing to learn. That's pretty much all it takes. The rest can be learnt from reading manuals like Barnetts and Sutherlands and the rest by doing. You might want to consider that the pay for such a job is probably extremely crap compared to what you'd make as an auto mechanic.