Page: It will hold name and value pairs. For Example, if you have a customer and you want to hold the properties like Name, age, SurName, Bank Account number, etc.. you will use a page.
Ideally you will use it to carry the data of a single record.
Pagelist: It will hold multiple page in a sequence. As metioned in the above example, if you want to get all the customers whose bank accounts opened in 2015, those will be multiple. So, you will use pagelist to hold all the customers. like customers(1), Customers(2) etc..
Each page will have that customer details like Name, age, SurName, Bank Account number, etc.. of that particular customer in each page.
Value: This is nothing but single value which will hold any property type such as text, integer, identifier etc..
Value list: It will hold string values numbering in series. Let me tell you with an example:
if any user updates work object in pega, you want to write an audit in to an external table(not in to pega tables.) This is for each operation which user is performing with some predefined values. In this audit you will hold 20-30 values. To hold these values create a value list.
Here you get a thought that, i can use page also. why value list. Yes. You can use. It depends on how you are getting the data. If you are using decision table to predefine values for each kind of operation, then Value list is correct option. If you are getting this predefined data from a table then Pagelist in the correct option. It depends purely on your requirement.