I'm the same way....I need to SEE it to understand it...and the Missouri Start Quilt Company as lots of great videos.
Also on this site, go to the links and resources to see tutorials. Watch some of them...I think just listening to the language they use and the things they do will help you to understand how to calculate better.
I hardly ever use patterns for anything I make - I get out the pencil and paper and diagram it myself - adding in the size of my unfinished squares + the size of my sashing + the size of my borders = my total. I do that for the width and then I do that for the length...and then I tell myself that a yard of fabric is 35" x 40" (rounding numbers for easy division)...and go from there.