I'm a little slow on servers. Is it correct to assume that with my apache server someone can view a webpage going through my IP address to my box while I'm using my computer to do something else?

How would this be done if it is possible?

If they have a route to your IP address, and you have open access to the HTTP port (normally port 80) then yes.. If your IP address is not static then presumably your ISP will sort the DNS side of it out.. Cliff