HTML layouts is the concept of design of web pages according to your requirements. It makes a better for looking at user ends. HTML layouts is used different type of elements of create web pages these are given below:
<header>- It exist at the top of the page. It is used to add heading on the page.
<nav>- It contains different types of link element to access different pages.
<sidebar>- This portion exist at left and right position of the page.
<content>- This is the main part of the pages which has complete information regarding to the web applications.
<footer>- It exists at the bottom of the page.
HTML layouts make any page attractive and as per client requirements so it is very important for web designers. If you understand concept of page layout then you will create many pages in differents layouts. I hope it help to design web pages according to your requirements.