Ok, here is my quick start guide using gfjardim's template which makes the rest of the process look pretty simple (so far).
The paths listed below assume that you are using user shares, if you aren't replace /mnt/user with /mnt/disk1
Click on the Docker tab.
Where do you want to store the Docker image? If you have an SSD, put it there. This image will probably keep your drive from spinning down. Put that location in the Docker image text box with a file name. (The grey text is just a place holder so you can type there) I use /mnt/cache/docker.img
(this docker.img file is like an iso file, and is actually mounted on your unRAID server.)
Default image size, keep it at 10GB, read in the forums for reasons to increase it.
Template repositories, this is what makes docker easy for us unRAID users, you can find a few template repositories throughout the forum, but a pretty good place to start is gfjardim's https://github.com/gfjardim/docker-containers/tree/templates
Click Save. Then click start
Click the Add button (The big green circle with a plus in it)
Drop down the Template selection and select Crashplan
Since everyone should be backing up data, I'll start with Crashplan.
Read through the description
Container volume is where you can access the Host Path inside the application
Leave the /config line alone unless you really need to change it. (This is where Crashplan configuration files are stored)
on /data Container volume set the Host path to /mnt/user
Click Apply
You should now have the Docker Container you just setup listed under Docker Containers. Notice there is an Autostart checkbox that you probably should check so you don't have to start the container everytime you restart your unRAID NAS.
To finish setting up Crashplan, refer to this forum thread http://lime-technology.com/forum/index.php?topic=33864.0