Beginner PHP question

For some reason sample website I have displays PHP variables in the
web browser. Also, hyper link i have on the page is displays like$page&id=$codeno

But there are some part of code does works fine. May be anything
inside <?= tag is being displayed in the browser

I know that <?= is like response.write in ASP or <?echo etc. but I am
a newbie and looks like I am missing something