A 3-d mesh is a collection of polygons that make up a shape.

A mesh is made up of vertices, edges, and faces. Today you will find out about the different meshes in Blender.
Start Blender by double clicking the icon.

Press the X Key to delete the cube. Click Erase
selected object. 
Up at the top of the screen click >add >mesh. When you
do this a list of different meshes appear.
plane -

cube -

circle -

UVsphere -

IcoSphere -

Cylinder -

Cone -

Grid -

Monkey -

Torus -

Add each of these meshes to your project by clicking >add >mesh >(the mesh you want)
Here are some different things you have to try:
Extrude a half circle:
>add >mesh >circle
At the next window click ok.

Press the A Key. All the vertices turn pink.

Press the B Key once. This gives a selecting tool.
Drag a box around half the vertices.

If you do this correctly half of your vertices should be
yellow.

Press the X Key. Click vertices.

Now you have half of a circle.

Press the A Key to select all the vertices. They will all turn yellow.
Click View. Click Front.

Press the E Key. Click Only edges.

Move your mouse up a little and click.

Click your mouse wheel and move your mouse. This
changes the view.

What could you do with this shape? Here is what I did.

Could you make the following:
car
stick figure
chair
table
house
animal
motorcycle
bedroom
stereo
television