Embedding variable in HTML from another c# class

[panicc.co]

I am new to JavaScript, HTML, C# so bare with me...I am using an ASP.NET framework. Within my welcome page (after a user logs in) I want to customize the paragraph text to include their login information. For example:\[code\]<p> Welcome to the website!</p>\[/code\]Is what the code would have currently, but what I want is:\[code\]<p> Welcome <var=Username> to the website!</p>\[/code\]Now obviously that is not correct, i didn't expect it to be. I just want to demonstrate what i am trying to do. I thought about using JavaScript to accomplish this somehow, but that seemed a bit overly complicated. My variable "Username" comes from another class in a .cs file elsewhere. How can I embed that variable into my \[code\]<p></p>\[/code\] ? Thanks.