Help me, How Select multiple items from ListBox and insert into Database in separated rows

  I have 3 tables (users - Project - User_Project ), when create new project , I want the user to be able to choose 1or many users  
and insert the selections into a table called User_Project .

select users from listbox.

Tables :

users :

user_ID :

User_Name :

Projects:

Project_ID:

Project_Name

User_Project

user_ID :

Project_ID:

 
...