Checking your server configuration is a review of the environment the installer is running in.
If any problems are reported in the Requirements section, these need to be corrected, otherwise XOOPS will not work.
The Recommended extensions section indicates additional PHP extensions that XOOPS, or XOOPS modules, may use to provide additional functions. You can proceed with the install, even if extensions are not available. But, if you can enable these, that is recommended.
After reviewing, select the "Continue" button to proceed.