Complex sentence: Most web based DDNS services use a standard user name and password security schema and require that a user first create an account at the DDNS server website and then configure their device to send updates to the DDNS server when an IP address change is detected.
Split into simpler sentences: Most web based DDNS services use a standard user name and password security schema. This requires that a user first create an account at the DDNS server website and then configure their device to send updates to the DDNS server whenever an IP address change is detected.