creating fixed updatable areas

Hi,
I’m trying to set up a website using WordPress for a friend. I want to set it up so each page is made up of sections that can be individually updated using the dash board, I then want to have all these sections spread out over 3 columns but all fixed. I am pretty new to this and have been trying to do this with posts but to no avail, maybe I just lack the terminology or am I going about this all the wrong way.

thanks