Hi there,
It's pretty difficult to explain how Hash Variables work in general with so little to work with but I'm gonna try my best guess at what you're trying to accomplish (and explain a simple use case).
Let's say you have a formA (formId: formA | tableId: tableA) and in it you have a field with fieldId as field1. Now suppose you have this form mapped to an activity in a process. In this case, whenever this form completes, joget would create a table app_fd_tableA in your database and against the processId (as the primary key), it would store the value of your field1.
Now consider we need this value to populate some field in another form (formId: formB | tableId: tableB) in the same process mapped to any other activity, then configuring the required field of formB to the value #form.formA.field1# would fetch the value of your previously entered field (note that since the process is same, joget would query the table with the processId as the primary key) and show that value in your field.
Hope this would help in some way.
Thanks!