Inserting data to junction table

example, I have a table like books and I have a table like authors and a junction table (many yo many).

cf 2018 and MSSQL 12

I can create form and insert a book in the books table. (no problem here)

Question is; How do I add  a record or records in the junction table? Also, How do I setup the form to input multiple records for the junction table.<thanks>