What is the Grid Theory and why is it important to web design?: 

The Grid theory is a simple version of the rules of thirds. Its important because with the grid theory you can implement it in any design so that you can see if the design is well balanced. With this you can check to see if your design has equilibrium. 

In addition to “balance,” what are the other design principles important also to Web design?

In addition to balance there is Unity and Emphasis.. Unity is important because with it you can have a sense of being organized.. you can have things grouped rather than to have things scattered around. Emphasis is also important because its important to have a focal point in a website where the user is mainly attracted to and that way the user will stay in the site for longer. No Emphasis and the user will surely leave the site because there was no intrest. 

What are the “Bread and Butter Layouts” in web design?

The “Bread and Butter Layouts” in a design is refered to the main 3 layout types..

1. right column navigation 2. left column navigation 3. Tree column navigation 

Facebook

Type: Social Media Website

Audience: Everyone

Goals: To let everyone and anyone meet new people and socialize with friends.

Amazon

Type: E-commerce Website

Audience: someone who likes to buy items on the net

Goals: To make it easy for everyone to buy online and sell online.

Google

Type: Educational / Entertainment / News / .. 

Audience: Everyone

Goals: A search engine that gives information of everything.