Because it might be hard to understand that the "ь" makes the letter before "softer", I would say that the "ь" is like a little "y" sound. For example: "ньо" would be more of a "nyo" sound. Another: the word "есть" is pronounced "yesty". The "ty" at the end is not a "ti" sound, but "t" then "y" like in "tyo" without the "o" ending. It is hard to explain, but you can definitely hear a difference in pronunciation.
If you see somebody drinking, you can ask "Что ты пьёшь?" meaning "what are you drinking (right now)?"
If you talk with friend and nobody is drinking right now, then "Что ты пьёшь" will mean "What do you drink (usually)?".
Well, Russian language has only 3 tenses (past, present and future), so the context is very important. But, you know, it's pretty hard to Russians to study English tenses too =) Because you can guess what tense you should use only by context, and that's very strange to have a LOT of tenses %) So just relax, the identify-context-skill will become better with some practice =)
It's not uncommon (I'd say normal, even) to add the (often implied) pronoun, either for emphasis, or just because.
It's true that more often than not there's no need for the pronoun when using the present form (as all forms are different), so I can imagine that this happens by analogy with the past, where the pronouns are essential. Or maybe it's just a formal/informal thing.