Becoming literate in English means not merely knowing the alphabet and grammar, but knowing the vocabulary, and the major works of literature in the language.
Much the same is true of a programming language. Learning the lexical syntax, the grammar, and the language semantics is a good beginning, but to be truly proficient in the language you need to also be familiar with a variety of standard libraries.
You now have a reasonable grasp of the Mythryl syntax and semantics; it is time to start learning your way around the Mythryl standard libraries, which provide much of the functionality you need to code effectively in Mythryl.
The Api Index is a good place to start your browsing.