Is it gde in the regular alphabet? I think that makes sense though, because in Cyrillic it's где (three characters). The "e" in Russian is sometimes pronounced "ye", and that's just Russian being Russian. It's like Swedish sometimes pronouncing "g" like a "y" in English, or German pronouncing "w" like a "v" in English.
As explained in Lesson Tips and notes , ты is used as Informal 'you' which you can say to your friends and family. While вы has dual usage, first one being as plural form of you (you all) and the second one being usage for elderly in a more formal and polite way.
Actually, this feature exits in many languages. In spanish, 'Tu' is the informal you and the equivalent of вы will be 'Ustedes' while in my native language Hindi, the counterparts are 'Tum' for informal you and 'Aap' for the formal you.
гДе*, а не гЛе. Где ты? sounds like a general question, while Ты где? puts more emphasis on the "where" part - maybe if someone says they're on top of the mountain you'd say "Ты ГДЕ??" (to express disbelief); or, say you're supposed to meet someone at a park and they tell you they're there already, but you don't see them, you might ask "Ты где?" to specify their location.