MijoACL is easily installed as any Joomla component. That should be done through your site's backend.
Once you log in, you should open the Extensions => Install/Unistall section and click on the [Browse..] button in the Upload Package File section. Navigate to the same MijoACL file you have downloaded earlier and select it. Then click on the [Upload File & Install] button to start the installation. It will install :
1. The main MijoACL component
2. Back-end & front-end search modules and quick icons module for back-end
3. Language files
4. Installer adapter that will enable installing MijoACL extensions via standard Joomla installer
5. Database tables (#__mijoacl_extensions, #__mijoacl_rules, #__mijoacl_permissions)