One tailed or Two tailed only, question, something, different

soverby

This is sort of a newb question, but when they are asking us to test if X is significantly different from Y blah blah we are supposed to use two tailed, and if they ask us to do a confidence interval like X +- (t value)(Standard error) , we use two tailed also.

We use one tail for F stat only?

I know you use one tail when you are testing if something is greater than or less than, and two tailed to test if it's equal to something.