data elements vs. data types

Hi,

I've created a table using SE11, but when I try to display using SE16, it states the table is not active in the dictionary. What does this mean and how do you activate the table?

Also, what is the difference between a data element and a data type? I can understand designating a type (c, p, f, etc.) to a field in a table, but I do not understand what a data element is. My ABAP book gives no explanation either.

thanks.

Kevin