Do you want to draw a simple clipart-like eye with Inkscape?
First, let's see how the final result will look like:

The first step is quite simple: draw three ellipses, one black and two white ones

You will probably want to rotate at least some of the elipses: click twice with the "Select and transform" tool on the ellipse to enable the "rotation" arrows.

You can set the color of the ellipse by clicking on the color toolbar at the bottom of the window.
Put the small white ellipse on top of the black one, select both ellipses and combine them with Path > Difference to make one single shape out of them.

Put the irid / pupil on top of the big white ellipse ("the eye")...

Click on the white ellipse, duplicate it (Edit > Duplicate), add the irid to the selection by clicking on it while the shift and alt key are pressed (the shift key extends the selection and the alt one allows select an object below another one covering it).
If everything is correctly selected, Path > Intersection will remove the "overflowing" part of the irid, delete the duplicated big ellipse and let the original big ellipse show up again, below the irid). If you get a "wrong" result, you can use the undo function (ctrl+z) to go back to the previous shapes.
Finally, since you want two eyes, duplicate the result, mirror it (Object > Flip horizontal) and move it to the right with the right arrow key.

Ah, no, that was not my final goal... I wanted to draw a turtle!

Isn't it cute?
P.S.: if you prefer it as a video, here it is!
(:youtube 3we-cWz2RIg:)

Comments
Ciao Alessandro ho aperto un piccolo post con il tuo tutorial sul forum italiano.
Ciao buonagiornata
http://inkscapeforum.it/international-section/drawing-a-simple-eye-with-inkscape/
Instead of using Path>Intersection, an alternative that can be useful sometimes is to use a clipping path it instead.
Put all three ovals into roughly their final position, but don't do the Difference or Intersection steps. Copy the large oval to the clipboard, then select all three ovals and group them. Edit>Paste In Place to put the large oval back on top of the group, then select both the oval and the group. Right click and choose "Set Clip".
This has the advantage that you can still double-click to enter the group to move the iris and pupil around, which is useful for fine tuning, or if you're trying to produce a series of images for an animation.