To perform complex tasks a helper method is used which includes code and markup.
If you want to perform perticular common tasks on different-different pages in your website, you can use a helper.
Though there are multiple pre-defined helpers present in ASP.NET, you can create your own custom helper too.
A helper enables you to use a common block of code across multiple pages. Lets take an example, suppose you want to create a title item that's placed on upper portion of your website and is must be visible from every page. You can create a <div> element with some <Label> that you want to show as a title with proper styling. Instead of adding this same markup/code in each page, you can create a helper and put the markup/code in it. You can then display the title with a single line of code on any page you need.
Makes code simpler, easier to read and maintain because if you need to change the title contents, you have to change the code only at single place.
You can go through this URL for more details:
Hope it helps.