When setting up an SMTP server a Master Admin will have the ability to Make this deliverability channel available to all my team members. With the same deliverability method you will only need to punch in your SMTP credentials, and all users will be ready to start sending emails with your own SMTP server.
Before checking this box you will want to check with your SMTP provider to see if the same credentials can be used for multiple users.
Services like Gmail SMTP and Outlook SMTP do not allow you to establish multiple connections with the same credentials. If you would like to get your users set up with either of these you will want to have each user input their SMTP settings and login credentials on the SMTP configure page.