First, I must mention we don't usually assist users trying to implement their own OIDC clients, as explained [here](https://www.gluu.org/blog/limiting-openid-connect-community-client-support/). So if you would like to still have some level of support as a free user, you should try to stick to one of the client implementations mentioned there, of which Apache's mod_auth_openidc seems like the most straightforward free option. You could also consider buying a license for our own oxd server package, which comes with [PHP libraries](https://gluu.org/docs/oxd/3.1.4/libraries/languages/php/) that should allow you to integrate it into your app.
Regarding endpoints' location, you should always consult OP's metadata, which is at `https://your.gluu.dns.name/.well-known/openid-configuration` But without understanding which role each of them plays, it won't help much, so take Michael's advice and study the specs document to understand the sequence and composition of requests and responses your app will be dealing with. Again, we can't help much here, within the scope of Community Support.