Encoding a chromosome: A chromosome should in some way contain information about solution that it represents. The most used way of encoding is a binary string. A chromosome then could look like this: 

Encoding a chromosome

Each chromosome is represented by a binary string. Each bit in the string can represent some characteristics of the solution. Another possibility is that the whole string can represent a number.

Of course, there are many other ways of encoding. The encoding depends mainly on the solved problem. For example, one can encode directly integer or real numbers; sometimes it is useful to encode some permutations and so on.