Open a new document in Maya and under the File menu, goto Project New...
In the New Project dialogue, Name your project shroom and for a Location browse to your local directory where you are keeping your Maya projects [My Documents/maya/projects by default]. At the bottom, click the Use Defaults button. If you do this with every new project, you will have a consistent file structure that will make your life much, much easier.

QUICK TIP:
If you are working in an environment where your system settings are reset when you log out of your machine, copy your prefs folder [usually found in My Documents/maya/ ] to a safe location when you are done for the day. Then copy it back to overwrite the default prefs next time you sit down to work – then you can keep your favorite settings.

Now for the fun stuff...

Create a Nurbs Shpere. In the INPUTS section of the Channel Box, set the number of spans to 5.
With your sphere selected in Object Mode, hold down the r-mouse button and select Control Vertex from the subcontext menu that pops up.
Highlight the lower of the middle ring of CVs with your move tool and scoot them up along the Y axis a bit. Then scale them in to make a tight ring like pictured here.
Now grab the CVs for the row above - they should be the widest spread row at this point. Pull them down so they create a hood over what is now our mushroom stem.
Head up to to the second to the top row and scale out the CVs. You might want to pull them down a bit too. This is where you really define the shape of your mushroom cap.
As a finishing touch, take the bottom two rows of CVs and scale them down flat together. That'll give us a nice base.
		now off to making our shader! > >