I just learned how to use the editor this week, so here's how I recommend doing it: Here's the links to the most important articles for learning how to code items and variables, though really, all of the articles on the Help & Info page should be useful. I recommend that after you read an article, you spend some time in the test-game that Zake suggested messing around and getting comfortable with the new systems.
How to use variables
How to use items
How to use link and variable restrictions
How to use the advanced editor
After you're comfortable using the advanced editor, you can check out some of scripting articles on the help & info page, as scripting will offer you a lot more options and flexibility when coding.
Specifically about your health potion question, here's how I would do it. (I think I said something like in the thread that got deleted, though I can't remember for sure. Apologies if I'm repeating anything.)
0) Make sure you're using the advanced editor. (You can activate the editor by clicking "Change editor features" on the "Story properties" page.)
1) Make a variable called "Health".
2) Make an item called "Health potion".
3) Set the "Default effect" for the health potion to take you to a page called "Use health potion".
4) On the "Use health potion" page, write a quick description about how drinking the potion makes you feel better.
5) Put one link on the "Use health potion" page, and have it be a "Previous page" link that says something like "Back to the game."
6) Click the icon with the cross on the "Back to the game" link to cause changes to variables from clicking this link. Make clicking this link cause the health variable to increase by however many points you want.
7) Click on the bag icon on the "Back to the game" link to cause clicking this link to make you drop items. Make clicking this link cause you to drop the health potion.