Question

Can someone help me with by explaining normal distribution and t distribution I am confused

Answer 1

we use Z when sigma is known, irrespective of the sample size, and we use t if sigma is unknown

Answer 2

on addition to wat "@matrix65" is saying u also use t in n<=30 and sigma being known.
another important point is that if u found that n is large (n>30) and sigma known u normally approximate it (it means u use z)