When to use one tail test and when to use 2 tails test?

When testing for the significance of a coefficient of a variable, when do we use 1 tail and when do we use 2? I am confused :frowning:

If it says that it equal to a value then use 2 tails And when it says that is less than or more than a value then use 1 tail.

You champion idreesz! Thank you!