IdentityServer publishes a discovery document where you can find metadata and links to all the endpoints, key material, etc.

You can use the following clients (see here for the code definition):

client id: native.hybrid
grant type: hybrid with PKCE
allowed scopes: openid profile email api offline_access

client id: native.code
grant type: authorization code with PKCE
allowed scopes: openid profile email api offline_access

client id: server.hybrid
client secret: secret
grant type: hybrid
allowed scopes: openid profile email api offline_access

client id: server.code
client secret: secret
grant type: authorization code
allowed scopes: openid profile email api offline_access

client id: implicit
grant type: implicit
allowed scopes: openid profile email api

client id: implicit.reference
grant type: implicit
allowed scopes: openid profile email api

client id: implicit.shortlived
grant type: implicit
allowed scopes: openid profile email api

client id: client
client secret: secret
grant type: client credentials
allowed scopes: api

You can call a test API at https://api.identityserver.io/identity.