dem - How to create contour lines from point data using QGIS?

I'm using QGIS 2.4.0 and I have a shapefile of points with elevation data and X and Y coordinates. I'm using windows 7 OS.

The idea is to create a contour line SHP using my point data.

My question is: How do I start working on that issue? Is there a function? Is there a step by step process?