Hello Mary,
I have created People entity and attribute UserId as Foreign key to map with User table.

Here is Interface Flow from Login client action we navigate to Signup Screen and created one more Screen to show Users Listed.

On Signup Screen in RegisterOnClick client action we need to create functionality that save user data and people data in respective database table.
- First as you know drag and drop EncryptPassword Run Server Action enter username and password from local variable "User" created on Signup UIScreen.
- Second drag and drop Assign and encrypt that password.
- Third drag and drop CreateUser Run Server Action and give local variable "User" as Source.
- Fourth drag and drop Assign and assign User.Id=CreateUser.Id.
- Fifth drag and drop Assign here now we have to assign People.UserId=CreateUser.Id before calling CreatePeople Run Server Action.
- Sixth drag and drop CreatePeople Run Server Action and give local variable "People" as Source.

Signup UIScreen register button carry main logic discussed above.

User Database
Details are getting saved in user table from Signup form.
People Database
Details are getting saved in People table from Signup form.

Login UIScreen
We can login Successfully from Login UIScreen.

UserPeople UIScreen
Details of Registered User and People Detail are shown.

Regards,
Ayush khare