Having "you" be the same for singular and plural can occasionally be confusing or at least ambiguous.
So many native speakers have come up with ways to differentiate them, e.g. using "you guys" or "y'all" for an explicit plural.
That sort of thing is usually regional; there is no univeral distinction between singular and plural.
"er" is [ɛɐ̯] or [eɐ̯] while "ihr, Ihr" are [iɐ̯].
So the second element is the same but the first one is either like "e" in German "Bett" or "Beet", or like the "ie" in German "bieten". (Or like the "e" in English "bet" and like the "ee" in English "beet", respectively.)
trinkst is the verb form for du (i.e. when you are speaking to one person).
If you are speaking to multiple people, then the word for "you" is ihr, and the verb form for ihr is trinkt without the -s-.
"She drinks tea" would be Sie trinkt Tee.
In this case, the er, sie, es and the ihr forms of the verb are the same (sie trinkt, ihr trinkt), but this is not always the cases -- for example, sie isst but ihr esst, sie gibt but ihr gebt, sie ist but ihr seid, sie hat but ihr habt.