U ar right Catkin.
Many vowel phonemes are not simply single sounds, as u can tel by how your mouth moves.
The single vowel sounds are just
short a, e, i, o, u and oo (at, end, in, on, up/oop).
The others (ai, au, ee, ie, oe, long oo, ou, yoo, oi, ar, air, er, ir, or).
In more phonetically spelt languages like Lithuanian or Finnish u learn them as such for spelling and they are pronounced as they are written: a-u, a-i, e- ...
In English this is more difficult and also less useful because of the many overlapping spellings (how, slow; cut, put; her, third, early, journey, turn).