i - is a sound between EE in mEEt and I in Is.

o - like O in fOr, or in the Scottish NO, or AU in AUght.

u - like OO in bOOt, pOOr.

a, e, i, o, u are all simple sounds, that is, the mouth is kept in one
position while they are being sounded. In learning them lengthen them
out, and be careful not to alter the position of the mouth, however long
they are drawn out. In the compound sounds given below the shape of the
mouth changes; to get the correct pronunciation sound each letter fully
and distinctly, gradually bringing them closer until they run together,
when they become almost as follows:--

aj - nearly like AI in AIsle, or I in nIce, fIne.

ej - nearly like EI in vEIn.

oj - nearly like OY in bOY, or OI in vOId.

uj - nearly like UJ in hallelUJah.

aux - like AHW, or nearly OU in hOUse, pronounced broadly, haOUse.

eux - like EHW, or EY W in thEY Were, AYW in wAYWard.

Practise saying aja, eja, oja, uja, auxa, euxa several times quickly.
Then gradually drop the final a.