HElp me pppppppppllllllessse

[العنيبي]

Is there any rule to help me. How can I decide the right way when I read u as a vowel or as a consonant sound
Us u is vowel
Use u is consonant
Look at these words can you tell me way
Study student upon absolute museum because sure rude tune


Do you agree with me that there is no rule / just we have to read them as we hear them

[Beauty]

there is not any rule says that the vowel sound pronounced as vowel and consonant at the same time

[العنيبي]

So can you tell me why we say
a unit
an umbrella
a university
as you know an used with a vowel sound and a used with
a consonant sound
So why we used a or an with u letter