Hanna, let me give you a bit of advice.
I don't think that trying to learn the grammar book by heart will do you any good. Well, not much anyway. Learning takes time, no doubt, but learning the formalized rules will make your mind carefully and thoroughly analyze everything you hear or see then it would look through your 'grammar database' in your memory, and then it would try to put all of that together at the same time being afraid that you might have forgotten something. Being afraid is a part of any failure in any task, by the way. Trying to do this consciously is very tedious and you'll yawn all the way to the point you'd abandon the whole thing.
Instead, let your mind learn the way it likes more - like accumulation of experience. I mean reading. Just master some basic vocabulary (some 500-1000 words) then take any book and Russian and start reading. Don't even bother to look for the unfamiliar words in a dictionary if the general sense is clear to you. Use the dictionary only if you don't understand completely what the sentence is about. After seeing that particular unfamiliar words in, say, 100 or 200 different contexts you'll know its meaning intuitively and that's when you need to look it up in a dictionary.
It would also be nice to get some audio-books (with printed originals) and read as well as you listen to it. I repeat - the key is to expose yourself to hundreds of different combinations of the same words. I know I learned English this way. I sometimes use words in English I learned intuitively without knowing the exact Russian meaning of it, because I never looked it up in a dictionary. As long the meaning of the phrase is clear to you - don't bother with some words - their meaning will come to you later.
I'm not saying that grammar rules are unnecessary I only say that if you have encountered a few hundreds of examples (your eyes would remember them at least) in a text, some of the grammar rules will be obvious to you.
Try it. Perhaps you'll find learning a bit more entertaining and efficient.