PCA and orange software I am analysing if 15 books can be grouped according to 6 variables (of the 15 books, 2 are written by an author, 6 by an other one, and 7 by an other one). 
I counted the number of occurrences of the variables and I calculated the percentage. Then I used Orange software to use PCA. I uploaded the file. selected the columns and row. And when it comes to PCA the program asks me if I want to normalize the data or not, but I am not sure about that because I have already calculated the percentage - is normalize different from calculating the percentage? Moreover, below the normalize button it asks me to show only:... and I have to choose a number between 0 and 100 but I don’t really know what it is.

Could you help me understand what I should do?
Thank you in advance
You should normalize data but you dont have to. If you dont normalize your data bigger range data will have higher effect on the model.

Just draw a box plot to compare the ranges of your data. If they have different ranges (like 100->200 and 1->10) you should definitely normalize your data. (Like mean normalization)