The best way would probably be to work on a language that isn't context-free. When you run into the problems context-sensitivity introduces, then you'll really start to understand it.
In the past, Pascal was widely used in teaching contexts, for both learning to program and later how to implement a compiler. I've seen Walter say in the past that he got into doing languages from a series of articles in Byte magazine that included the listings for a small Pascal compiler. For your task, you can use Oberon instead, which is a smaller and simpler than Pascal. Oberon-07 is context free up to a point, which is another way of saying that it's not context-free. It'll work well for this exercise. Don't worry about writing a full-fledged compiler, because you'd end up spending forever on the code generator backend. Instead implement half of a compiler.
Here's one project that fits the description of being one half of a compiler—a documentation generator:
Implementing this requires doing the lexer and the parser, but its "backend" streams out documentation pages instead of object files or assembler. The truth is, you wouldn't even need to go that far. Just do the lexer and then start implementing the parser—let's say that your program should just read in source code and then say whether it's valid or not—whether it will parse. Since Oberon is mostly context-free and the natural way to do things is to use a recursive descent parser, you'll get into a rhythm implementing things, until you run into the part that's context-sensitive, at which point things will get uncomfortable. You will find true enlightenment then. This can be done over a weekend, but if you reach the end of the first weekend and realize it will take you two, don't sweat it.
> I mean I want to make a useful language, is being context free practical?
It is. If you do the exercise above, it should be straightforward to figure out several different ways to change the grammar to eliminate context-sensitivity in your parser. You'll realize that the transformations would be minor. They won't compromise the power or practicality of the language, and it's possible to end up with one that is almost exactly the same. The biggest casualty in this case would be reworking a dubious design decision made for aesthetic reasons.
> Any programming language that is massively adopted is context free?
I want to have an intuition on what is context free and what is not.
Is D context free?
I mean I want to make a useful language, is being context free practical?