Translation:I do not draw pictures.
While both "書く" and "描く" are "かく," the kanji used in the first one does not refer to drawing in an artistic sense. It would refer more to drawing in the sense of drawing out Kanji characters for writing (if it were to refer to drawing at all). As for "描く," it is both "えがく" and "かく." There are two different readings for it that are identical in meaning.
書き and 描き both read as かき and mean to write. 書き being used in a more literal sense and 描きbeing used in an artistic sense.
In this use えが描きwould literally translate as "to write pictures." In English though, that would be weird to say so we change it to draw. That's what I took away from it at least.
If you used を "you" would be the implied topic of the sentence and further conversation would continue to be about you.
By using は here, it's making "pictures" the topic for whatever reason. Kind of like, "As for pictures, I don't draw them." maybe you plan to follow up by saying you just like to look at them instead or something.
Potential form of the verb( can, cannot form of the verb) has separate Conjugation rules(which Duolingo hasn't taught yet) . So here it is not "can't write"
Now there are no separate Conjugation rules for future and present form of the verb. We decide between the two using context clues. Since we do not explicitly know the context, both "won't" and "don't" are accepted.
When is it acceptable to drop the topic of the question, as it is implied? For a previous question, I was asked to translate from Japanese to English, "本はあまり読みません" (I do not read a lot of books) However, I only answered "I do not read a lot", which I thought would imply the topic being the book. It was marked wrong, as you may have guessed. But here, the Japanese translation explicitly mentions the picture, whereas the English translation doesn't, yet it is considered right as the topic (picture) seems to be implied from the usage of "draw".