Secure User Homepage

I am trying to create a simple website where users can have usernames and passwords to login to a homepage that contains their information. How do I get the homepage to know which user is signed in? I know I could use a simple GET

 www.mywebsite.com/homepage?username=myUserName

But this doesn't seem secure. I could put this into a POST request but that doesn't seem secure either as anyone with the username could login and get the information. Do I need to include the password every time someone accesses the homepage? Or is there another way secure way of doing it?