Fatal error on install

Hi, I'm new to Grav, and i've just been trying to install Grav on my website, and this is what I get after I upload the entire folder of Grav using FTP, and try to access the page:

Fatal error: Uncaught exception 'RuntimeException' with message ''mbstring' extension is not loaded. This is required for Grav to run correctly' in /home/def0021/public_html/grav-admin/index.php:25 Stack trace: #0 {main} thrown in /home/def0021/public_html/grav-admin/index.php on line 25

I have no idea what this means, can anyone help?

Enable mbstring in your php.ini file

Here is a link to ensuring mbstring is installed configured and enabled,
http://www.knowledgebase-script.com/kb/article/how-to-enable-mbstring-in-php-46.html