This is rather simple and best told in pictures.  The first step is to open one's inventory.

Then:

One correction (updated 2009): SL now lets you copy/paste text FROM SL to, say, Word or a text-editor.  Thank goodness.

Then:

And finally:

To give someone a copy of your notecard, simply find it in inventory and either drag it to their avatar on the screen or open their profile and drag it there.

Scavenger Hunt Bonus: 50L to the first student to leave Ignatius a Note Card.