Basically you need look at your design in order to determine what would make most sense.
A very popular choice is to divide it into three equal sizes and then have one of them be the right or left column, while the two others combine to form the other column.
So you end up with two columns one for content and one for navigation (typical blog look)
Grids can obviously also be much more complicated as those used in photoshop, 3dmax, word or windows/osx.
If you want to get really into grids I can recommend probably the best book written about them.
You don't need a book. You just need to build a hello-world application with the Bootstrap CSS/JS code, using one of the layouts they provide as a starting point. Then just use the page of Bootstrap demos as an a la carte menu as you find yourself needing UI features.
The Grid Systems book that was recommended earlier is a better bet if you're a typographer or graphic designer, and particularly if you're thinking about designing novel grid systems. But you're not doing that. The Bootstrap grid is trivial and does not require any background in design to use.
All I can offer here is my opinion. I have the book. I like it, because I geek out a little on typography and graphic design (I am horrible at both). I wouldn't put the book on my "buy immediately" list of practical design books for developers.
_Elements of Typography_ (which also has some coverage of grids, along with meter systems), yes. _Elements_ is a buy-immediately book (and a joy to read).
Basically you need look at your design in order to determine what would make most sense.
A very popular choice is to divide it into three equal sizes and then have one of them be the right or left column, while the two others combine to form the other column.
So you end up with two columns one for content and one for navigation (typical blog look)
Grids can obviously also be much more complicated as those used in photoshop, 3dmax, word or windows/osx.
If you want to get really into grids I can recommend probably the best book written about them.
Josef Muller Brockman Grid Systems
http://www.amazon.com/Systems-Graphic-Systeme-Visuele-Gestal...