The difference between encoding and encrypting can best be explained in terms of mathematical functions...

When you encode a piece of data, d, you are applying a function, f, that is reversible by another function, g. Or, in other words, g(f(d)) = d... All the decoding requires is an algorithm.

When encrypting data (I'm going to simplify things) you have a function that takes several parameters and spits out encrypted data. In order to decrypt the data, you must also posess the other data to apply the correct function.