Required Field - Conditional Formatting

[#1]

Hello, I am wanting to set up a form so that if you select A then you're required to enter information into 1 but if you select B then you're required to enter information into 2 type logic. I am not very familiar with writing code but was hoping someone might be able to assist. 

[#2]

Hello, I am wanting to set up a form so that if you select A then you're required to enter information into 1 but if you select B then you're required to enter information into 2 type logic. I am not very familiar with writing code but was hoping someone might be able to assist. 

[#3]

"you're required to enter information into 2 type logic"

What does it mean?

[#4]

To clarify: What should happen if the field is not filled-in? In what sense is it "required"?