Yeah once you get your head around column and row it is SUPER easy.
If you want things to be stacked vertically (think like a header, a title, a repeating group and then say a footer) you want a ‘column’ element. And then it will just automatically stack one of top of the other and you can drag and drop the order of it, even add or delete elements without having to realign stuff…LOVE IT!
If you want things to be horizontally next to each other (like say a row of a RG), you want a row group…this way things automatically go next to each other (instead of stack on top).
You can easily set a large container group padding or margin and then not have to worry about the ‘x’ value of all the little elements as they’ll automatically line themselves up.
You don’t really have to set the exact dimensions of an element, just decide if you want it to change based on the size of the content, an absolute fixed width, or if you want it to respond to page width and other elements dynamically (you may set just min or max widths also).
Easy peasy 
Start with converting small things like your header or footer to get your toes wet, then do your smaller RE and then once you’ve got a bit more confidence start building pages from scratch
