I'm planning to use Material-UI CSS framework (http://material-ui.com) in order to design front-end of a website, but I don't have any idea about how to use this framework.
I'm not familiar a lot with NPM, Browserify, etc. I just need to know how shall I start in order to learn the way to use this CSS framework.
Thanks for any help!
Don't be intimidated by the (apparent) complexity of webpack and other (great) build tools, and don't be discouraged by envious jerks who say things like "To be honest, I think you got a big problem to use this stuff."
The reason why the material-ui implementation (usage) is based on these tools is because is currently the best way to write software and understanding this and other frameworks is a great way to learn why this is the "right" way, and become proficient at writing quality modular code.
Webpack, and the other build tools, exist for one purpose: to create one "main" file from your app's source code that can be read and delivered to your users' browser in an efficient manner. Long gone are the days when we would write a bunch of include (script) tags for every resource (file) we need in our pages and thus have our users wait until all these were downloaded from our server (or multiple locations e.g.: cdns) and then the page would load. The efficiency is based on the fact that you can deliver one (often minified/compressed) file that contains all your code and any code it depends on (e.g. React or even jQuery).
Build tools accomplish this by asking you 3 things: what file to start with (entry main file), what tools (loaders) to use to process non-native JavaScript code within your code (scss, jsx, etc) and what file to create as the result (converted and minified output). This output file will be the one you use in your html import/script tag. It will contain your code plus all other dependencies, which would be a nightmare to include and resolve manually yourself. Here is a good beginners' guide.
Material-ui, like many other frameworks (reason why I took the time to explain all of the above) is built with modularity in mind: pieces of code can be "glued" or "pieced" together like Legos, in order to easily build bigger parts. You do this by simply including the components you need in any component you create. They are React components which are a simple way to define (write/create) the "building blocks" of your site/app. There are tons of great videos and tutorials to get you started with React (my favorite is reactjsprogram.com by Tyler McGinnis).
To get you started with material-ui, they have created a couple of examples to get started using webpack. Follow the simple steps to install npm and the dependencies (you can find them in package.json) and open the /src directory in your editor. You'll figure it out in no time.
You are in the right track with the right attitude by asking questions, learning to be a good developer, researching and trying to find the easiest way to accomplish your goal.