membership plugin

Hi, Please can someone tell me the following:

If I use the plugin membership and enable it then is ALL of my site protected from any member of the public viewing it?

If this is the case then it means I need a specific membership site separate from my ordinary site.

If this is not the case then can someone tell me how to allow a member of the public to view my site and then decide if they wish to join and become a member in order to have certain privileges.

I do not wish to hide or un-hide content of my site – I just wish people to be a member in order to enjoy certain privileges.

Meanwhile I am clicking this and that and the other and signing off in order to see what Joe Blogs can see and cannot see on my site and it seems to me that if you have membership enabled then Joe Blogs cannot see your site – it is protected.

If you do not enable it then I think membership does not work at all.