Welcome to the forum! Some websites have certifications or tutorials but generally the guidelines for the specific shop you are performing supersedes anything you may have read or heard elsewhere. What you probably have seen thus far is your 'ICA' or Independent Contractor Agreement. That is the legal basis for your work for the company as an Independent Contractor. The actual report you will be filling out may range anywhere from a series of check boxes to substantial narratives, so there is no way we can tell you in advance what the paperwork is likely to entail without knowing which company you have registered with.
Generally shops are done alone. Your guidelines will tell you if you absolutely MUST be alone or if you MUST take someone with you (for things like restaurant shops for two, etc.)
There is a lot about how this works and getting yourself organized in the sticky threads at the top of the New Mystery Shopper section of the forum.