Somebody help!
When I press site administration i always get this screen. How can I avoid this situation...
Possibly a plugin or theme has been added or removed and Moodle needs to perform the install or uninstall steps for this but cannot continue because a required PHP extension (intl) is missing.
You must install intl, here's some more information.
You should also install xmlrpc, and installing and configuring OPcache will improve performance of the site.