Yes, it's very easy.
If not you've not already set up your Facebook account on your Hero go first to the Home screen then Menu->Settings->Social networks to enter your Facebook details.
To upload a photo: go to Albums, find the photo you want to upload, tap on the photo to select it, tap on the "Share" menu button* (looks like a dot with two arrows pointing NW and NE) then choose Facebook from the list of sharing options.
The photo file gets reduced in size and is then uploaded to a 'Mobile Uploads' album in Facebook.
*If you're looking at the thumbnails for an album (either in Filmstrip view or in Grid view) the Share icon should be visible at the bottom of the screen. If you're looking at an individual photo, press the Menu button to see the menu options, including Share.
In my experience the Upload doesn't always work first time, especially when I have no WiFi connection. I'm not sure whether this is a problem with the Hero or the Facebook website. In this case you get a "failed upload" notification which leads you to a screen where you can try again. It's always worked for me after 2 or 3 attempts.