Creating 'Mesh' shapes Effect through Illustrator/Photoshop

My advice is to follow Monika's advice, and create a grid using the Rectangular Grid Tool, which you can find by clicking and holding on the Line Segment tool. Make it a convenient size, and start with a grid dense enough to show you some apparent topography, but don't go overboard with lines until you begin to get the feel of it. On the other hand, you can't see much with just a rectangle. Apply an Envelope Distort mesh of no more than three or four lines in each direction. You can always add more later with the Mesh Tool. With the Direct Selection (white pointer) Tool, select a point, move it, and see what happens to the grid. Play with the direction handles by moving them toward or away from their origin point, or rotate them about the point. Do the same with more points to see how you can control the apparent shape generated by the now-curving lines of the original grid. Once you start to feel as though you know what's going on, click with the Mesh Tool (U) on a mesh line but not on a point to see what happens to the mesh. Then click in an open space within the mesh but not on a mesh line. Take note of how quickly it can get very complex. Mostly, have fun, and don't hesitate to ask more questions.

Peter