Rmagick Howto?

I have been trying to get rmagick working in my rails app. Everything I
try fails! I am able to run it okay from a *.rb file from my command
line, so I know its installed.

Are there any tutorials or howtos? I haven’t found anything good on the
web.

What I am trying is to upload an image from a form, create a thumbnail,
and store them in a db. I am able to upload and store the image, just
not the thumbnail.

Anyone have any recomendations how to do this?