Plugins not appearing in dashboard


I uploaded the domain mapping plugin & multi-domain plugin as per instructions. I also uploaded several others (none as yet activated).

Only the domain-mapping & multi-domain plugins did not appear on the dashboard - either network or individual dashboards.

I have deleted them and sent them to my web guy. I noticed in one of the unpacked files that there is a mu-plugins folder in the multi-domain. Is this an issue?

Web guy is trying to alter the sunrise.php as directed in another post - but it is difficult when it does not appear in the plugins!

Just wondering what the use of the mu-plugins folder (the one separate to the plugins folder) is anyway? It confuses me a bit when there is also this file in one of the unpacked plugins (see mention above).