From BlenderWiki

Mesh Selection

Mesh selection in Edit mode is both a complex and crucial topic. Complex, because even the simplest models can quickly have hundreds of vertices (i.e. of selectable elements) – and for heavy detailed models, we talk of tens of thousands or more! So selecting exactly what you want can quickly become a headache. And crucial, because it’s likely you are going to spend a great amount of your time with Blender modeling meshes objects, so you’ll need to be most efficient!

So, first, we will see that you can select different kinds of elements (the one described in mesh structure page), using the select modes.

Then, we will discuss about “general” basic and more advanced (like some of the Select menu options) selection tools.

And finally, we will talk about advanced selection tools that are specific to edges and faces.