Integrating WordPress Log in with My Website

I am new to WordPress(WP) that said I am trying to add WP login to my website which isn’t built in WP. The big picture is to have a login on my website and able to restrict access to certain content depending on user’s level using WP or Paid Membership Pro (PMP)(https://www.ads-software.com/plugins/paid-memberships-pro/) plugin.

For the start I just need help/direction on adding a WB login to my website, can anyone direct me to the right resources or provide me with perhaps better alternatives that I haven’t thought of yet to achieve the same goal.

So far I just look at https://codex.www.ads-software.com/Integrating_Wordpress_with_Your_Website

Are there a Loop for adding user login.