These are the most basic settings you must configure. Without these, you won't be able to use Simple LDAP Login.
These settings give you finer control over how logins work.
Most users should leave these alone.
Here's a brief primer on how to effectively use and test Simple LDAP Login.
The most effective way to test logins is to use two browsers. In other words, keep WordPress Admin open in Chrome, and use Firefox to try logging in. This will give you real time feedback on your settings and prevent you from inadvertently locking yourself out.
If you accidentally lock yourself out, the easiest way to get back in is to rename to something else and then refresh. WordPress will detect the change and disable Simple LDAP Login. You can then rename the folder back to its previous name.