When options like "Email Address Verification" (found under Admin panel → Settings → General → Mail) or "Enable Phone Verification" (under Admin panel → Settings → General → SMS) are enabled, users must verify their email address or mobile phone number accordingly. Users can not logged-in until users complete the verification process.
If only the "Email Address Verification" option is enabled, the user will able to log-in on the website once the user verifies their email address.
If only the "Enable Phone Verification" option is enabled, the user will able to log-in on the website once the user verifies their phone number via the SMS code.
If both options are enabled, the user must verify both their email address and phone number for the user will able to log-in on the website.
If none of both options are enabled, the user is automatically logged-in after his registration, and may log-in on the website without any verification.