What can I do if I was wrongfully accused of stealing from a big retail store by the manager?
He was totally 100% wrong. I also have documentation - quick summary of what happen signed both by me and also a employee that works there.
1) If you are arrested and face criminal prosecution, you defend yourself, of course, presenting evidence and testimony that you did not steal.
2) If you are sued for what you allegedly stole, you again defend youself.
Remember: it's not enough that you are accused--the case against you must be proven, either by the state or by someone suing you.
3) If the store or a manager there is making public statements that you stole and you believe those statements are untrue, then that might be defamation--defamation is the public (so, to any third parties) making of untrue factual statements that damage someone's reputation. If you think this is the case, you may wish to speak with a personal injurry attorney and see if you have a claim for defamation and can seek compensation.
4) If they either press charges or try to sue you and the case is sufficiently weak--really nothing to it--you may even be able to sue them for improper use of process or malicious prosecution (basically, improperly using the legal system) and this is something else to discuss with an attorney.