I can't answer your first question as I'm not familiar with English Discoveries.
Regarding your second question: the purpose of communication and language is to be understood by the people we are talking to.
Consider your own language. In casual and rapid daily conversation with friends and family in your native Arabic, do you at all times take the trouble to follow the strict rules of grammar?
I don't think anybody in the world does. We all have our dialects, accents and regional variations of speech.
You ask if you have to care about grammar.
It all depends on whom you are talking to. At this very moment I am being extremely careful to write in grammatical English, because you expect nothing less from a teacher.
But when I go up to bed I might say to my wife 'Wonna g'shoppin t'morra?' (Do you want to go shopping tomorrow?)
You need to learn the grammar of a language if you want to communicate on a formal basis, but for casual speech with people who understand you - who cares?
Student or Learner