Ich Glaube Du Translates as I believe You are.
You are I.
Guten Tag, ich heiße Heiko, du bist freundlich = Hello, my name is Heiko, you are friendly
Wie alt bist Du? means: how old are you?
I hope you are the right Patrick.
Du bist hier on Internet
Ich weiß wer du bist.
bist du in Ordnung = are you okay
Ich bin - I am Du bist - You are Du bist ein/eine X - the use of ein or eine is dependant on the gender of the word X
ich bin comasch und du bist schiest
I'm there when you are.
"Are you with me?" That would be a translation of the question "Bist du bei mir?". The start of the sentence as in the Bach/Stölzel aria "Bist du bei mir, geh' ich mit Freuden" would be better translated as "If you are with me (or: if you're near to me), I go light-hearted (or: with gladness)".
Wie alt bist du= How old are you You answer with "Ich bin...." (I am...) Example: Ich bin zwanzig (20). Ich bin sechs (6). Ich bin neunundvierzig. (49) For more numbers & pronunciation of those numbers, see the related link below.