What is it meant by a normalized eigenfunction and how do you find it?

Question

I am doing a course called "Partial Differential Equations" and I was told to "find the normalised eigenfunction for": $$y''+ \lambda y=0,\;0<x<1$$ subjected to: $$y'(0)=0,\;y(1)=0$$ Ok, I know how to work that out. Just need help to understand what exactly makes it normalised. I thought you would check the orthogonal property, but for the second part he said "Verify the orthogonal property of the eigenfuntions." Is there like a condition you use that makes it the normalised version? Eg. finding the values for when $\lambda>0$?