Revit has two types of issues that it tries to make you aware of and deal with, the ERROR and the WARNING.
You cannot ignore an Error. It just won’t let you finish the task you are working on. You have to deal with it right then and there.
Warnings will actually tell you in the box that they “can be ignored”. Even though it says that, try not to ignore it. Try to remedy the problem right then and there. Why? Certain types of Warnings can REALLY slow down a model.
And if you “accidentally” skipped one, you can go back and find all your warnings by clicking the Review Warnings button on the Manage Tab.