Login System for WordPress

Hello there!

I am reasonably new to WordPress, and as a group project for my college course me and my group are making a website for a company.

The company in question wants the website to have a strict register/login system where the website is completely inaccessible unless you have the correct login credentials. By this I mean you cannot access any element of this website without being a registered user, and the registered user must be okayed by the site owner to be able to log in.

Does anyone on here have any information on how I could achieve this? I don’t mind delving into a PHP/mySQL solution to achieve this either, but also it is important that the site owner is able to manage user accounts in an easy way since he is not a web designer.

Any replies will be much appreciated, thank you.