How can forgery be used in crime

Some bad people will tend to forge dollar bills and make fake bills, giving them to cashiers and asking for it to be split into a different amount of bills so they are given real cash and wont be caught or they will buy things, return them and be given back real money and get away with it. This is obviously a crime because it's fake.

Forgery is basically the imitation of documents, contracts, Identification cards, or any legal certificate.

Imitated documents, contracts, ID cards etc can be used in any crime. And in many states forgery is said to be a fraud.

Anything can be forged and used in somewhere as an original document, certificate, ID card etc, which is indeed a crime.

Some common examples are imitating legal documents to have someone's property or business, using of imitated certificates to get jobs in companies, forgery signature on someone's checks to take out cash, etc.

These all are crimes.