How do we use fractions on this calculator??

You can use forward slash / as we write in a fraction.

6/2 is a fraction. And if there are more numerals involved, use brackets as (6*2+8)/4

I hope it helps.

with the $$\div$$ button

If you are doing calculations with mixed numerals it is best to put them in brackets like $$(3+1\div 2)$$

you simply make it a decmil if 4 were 1/4 i would put 4.25