To file a civil complaint, one need only allege a plain and simple statement of facts (without proving those facts), which, if true, would entitle the complainant to some relief (a monetary award, an order declaring the rights of the parties, etc.).
Here is an example of a short and simple statement of ultimate facts (as opposed to legal conclusions) that got a Virginia homeowner past a demurrer (motion to dismiss) by the bank-trustee in a securitized mortgage case.
Because this litigation is ongoing and the clients have chosen to maintain their privacy, only redacted versions of the documents are made available.
The redacted complaint can be accessed here.
The redacted order of the court is here.