Yes, with the new version 5.4 you get three basic designs you can start with.
Once you learn more, you can create your own designs.
Why would you keep more than one design? Well, you can apply a different design to a certain page alone, or a whole tree.
For example, when having a season, instead of changing the whole site's look and feel, you can use a theme for that particular season and in a part of your site only.
Hope this makes sense.

Thanks again Okhayat. The reason I asked was because as a developer you store the different designs and sites on you local drive for testing and showing prospective customers. I just wanted to know if I could store a web site once its finished and then start a new project say for a new customer and maybe if needed later retrieve the site for viewing or editing within C5. It sounds like C5 is restricted to one site per installation or have I misunderstood. I'm just used to the way I was taught in uni - the traditional way where all your projects are stored in separate folders and you edit them via your preferred editor and view them in a browser on the local host.

No thats correct - you run one concrete5 installation per site.

Thats too bad, what does everyone do if they have work for several clients?

please tell me there is a way to store the work done on one web site project and then load another web site project when required

Sorry, but I can't understand what you mean by 'store a site' or 'store a design'.
Do you mean using the same theme with more than one site? or applying it to different pages?

I mean work on a project and then save the site on file for later use or transfer, editing etc

My point is I have two sites to do this week and want to be able to work on both within C5

- You can reuse any code you developed (theme, block, single page.. etc) simply by copying it to the new site.
- You can have a backup of your site and restore it for reuse. Say you do the main configuration for the base installation you want, and simply backup/restore the data and use for a different site (with minor modifications).
- You can use the same /concrete core for many installations so you don't have to update many directories. still you need to update the DB for each installation, if any.
That's as far as I know ;)

thanks again