Ok so after your comments, when you add an "app" into a Sharepoint site, you can select to create a List (Think of a document library, without the documents), into which you will add columns with information (Metadata).
Sharepoint will create a new form based on the columns for the list, that is used whenever you add a new item into that list.
Picture 1 Example of an empty list with columns added:
Picture 2 Example of a new item being added into the list:
If you require more information on how to create a list and add columns into it, please refer to this Microsoft article. Good luck!