Some little corrections, if I may...
Well, It’ll be very short because my English’s not that good yet, I’m gonna try though!
Last March (the names of the months are initiated with capitals [letra maiúscula], always...
I decided [that I wanted] to do an English course cause I always liked it. [period here - ponto final aqui] Furthermore [além do mais/ademais] English is, certainly a thing you must learn nowadays, it’s not a choice.
Since march my English’s improved a lot! I’ve been learning many words and getting new vocabulary every day.
I think that if you are learning English you must not treat grammar as a priority in the language because It is not. What makes a language is  words not grammar, and if you try to get more words everyday your English’ll improve a lot.
Am I in the right path to learn English?
 Here it´s not about being right or wrong, just that I felt it could be terser, more concise, and a bit more natural English, perhaps.
 What makes a language is... However, you could write "what makes a language are the words"
Just a matter of using other word; to my thinking, it seems now more natural in this case.
Obviously, you are in the right track. To be honest, a pretty good work to a
5-month English learner!
This way you willl get good results, keep up the good work!
These corrections are minors, with time these minutes of English will be second nature to you, you betcha!