Need a good combination

I am new to developing webapps. Last week I participated in a hackathon with almost no experience. I made a simple web app using html css JavaScript. I used flask to run the app on server. I would like to know how is flask for beginners. And moreover I couldn't connect front end with backend. I found a couple of Google search results which mentioned something called jquery and ajax. What would be a good resource to learn more about it and other http stuff. Thanks in advance!