BASIC install of Marketpress by total newb

Hi,
I'd like to quickly preface this by stating that I am possibly the most clueless newbie customer of yours and there is a solid chance that you will not even be able to understand my question because I have no idea what I'm talking about.

oook! having said that, I have just become a full member of WPMU DEV because of the major appeal of your MarketPress plug-in.
I have a self-hosted website that at one point was totally fabulous because I was paying someone a lot of money to do it all for me.
It is now nothing but a boat load of error messages.
I figured out how to get my domain name back (yeah, I had to buy it at auction from god-only-knows-who for a grotesque price). It is hosted with GoDaddy and I used the auto install option for wordpress.
I have purchased and installed (and unistalled and reinstalled) countless wordpress themes thinking that something magical is going to happen and it never does... haha
I think this can be attributed to the fact that I have no concept of the relationship between wordpress and godaddy (and the things that accompany godaddy, i.e. ftp, databases, etc)

Ok, I apologize for rambling and here is my question:
Prior to installing the Marketpress Plug-in (which I surprisingly know how to do), should I do anything in godaddy or wp dashboard? Like, should i de-activate all my un-used plug-ins and kind of attempt to install as though I have just created my wordpress account? a clean slate, so to speak?

Last thing to note is that I have no content to worry about losing : )