Confusion about actions and attacks

Hi I just had a question about how actions are resolved. In the players guide (if I have read it right) you roll a number of dice and then equal to the attribute and then you add the modifier. What I understand from this is that you had all the D20's up together that were rolled and then you add the modifier if any are to be used. It then talks about how combat would work. What then confuses me is that in the combat section the highest roll is taken and that is used along with the modifier.

So which is correct out of the following;

All actions are resolved by taking a number of dice rolled and then using the results of the highest roll

Most actions are resolved by adding all dice up and adding modifiers, apart from attacks which use only the highest roll

Thank you in advance