How can I make a web app in Go?
Is there a way I can interchangeably use Go code and HTML like with PHP and HTML?
More specifically, what I want to know is how to get my PrintLn output to show in a web browser and how to accept input from HTML form fields?
You can't embed Go & HTML (for many, many reasons) but you can use Go's html/template package (http://golang.org/pkg/html/template/) to generate a HTML page from your HTTP handlers.
I'd suggest reading http://golang.org/doc/articles/wiki/ and using http://www.gorillatoolkit.org/ (routes, cookies, etc) for the web server side
You need to setup a web server in go and process http request/response as input/output. There is already an answer about go web frameworks which would be helpful. link
If you don't want your ui to show in a browser window, you will have to bind your own html engine. For that purpose you can look at ui frameworks like walk which has ie based webview builtin or engine bindings like go-webkit which builds a custom webview.