I'm a beginner (basics 1, basics 2, animals and doing almost done with food) but this is my advice
tu bois le jus isn't you are drinking juice, if you read the translation. It means you are drinking THE juice. If it would be just you are drinking juice it would be "tu bois du jus". Therefore, il parle le russe is "he speaks the russian" and the correct sentence would be "il parle russe"
Correct me if I am wrong :)
I know you are way beyond this now, but for others who are wondering the same thing: French does not have a present continuous tense--just one present tense. The simple "je bois" can be translated as either "I drink" or "I am drinking". There is an emphatic form as well, usually used in inversions to ask a question (we'll save that for later). So the French just say "je bois". If you want to emphasize that the action of the verb is happening at this very moment, there is another phrase (en train de) which is used with être for this purpose. You will learn about that in due time.