Let me show you how I created a simple web shop icon (shop trolley).
In Illustrator (or similar vector software) make a simplified shop trolley "L" shape (the handle + basis).
Now, we will select the basis line and copy it two more times to get something similar to E shape where the left vertical line end up above the top horizontal line. Draw one vertical line that will close the shape.
As for the wheels, create two circles below the basis of the trolley. Make one ellipse and then a second one, smaller in the middle of the first one. (Do that using Ellipse tool). Select both ellipses, and subtract them with "Pathfinder -> Subtract from shape area" option.
There is our wheel :)
Copy that wheel and position them under the basis.
Now for the background circle follow the same procedure as for the wheels.
One small difference is that holding ALT+TAB will make this ellipse a perfect circle. Color it, place it behind the trolley and - voila!
Let me know if you need any help.
The full tutorial that includes screenshots
Oh, and one last thing. I proudly announce that my CafePress store is now open!
Please check it out
Oh, one last last but not least thing, if you see any illustration in my portfolio for which you would like to know how it's done - let me know. I will gladly show you.