Open your habitcal.
Click on "switch to public view".
select the address with the mouse.
It should start with:
http://everydaysystems.com/habitcal/view/?o=.......
Copy the entire address (Ctrl+C on windows, or open the edit menu of your browser and click on "copy").
Then you can
1) insert the adress in a given message:
In the message editor, click button "URL". It should write "[url]" in your editor window.
Paste the adress (Ctrl+V on windows, or open the edit menu of your browser and click on "paste").
Click button "URL" again. It should write "[/url]" in your editor window.
So now you should have [url]adress[/url] in the message.
If you want to make it look nicer, edit it to make it look like this:
[url=theaddress]Please click here to see my habitcal[/url]
(PS: a simpler way is just to paste the address in the message. The above is especially useful when you want to make it look nicer by hiding the address and customizing the link's text)
2) insert the address in your signature:
click on "Profile" at the top of the page
in the "signature" field, insert your address with the [url] and [/url] tags as above except you have to write the tags yourself.