There are many ways to get your flash gun/strobe off of your camera.
You can use a cable or a optical slave cell these are cheap or a radio wireless trigger expensive.
In the shot below I have used a old Nikon strobe a SB-26 that has an inbuilt optical slave cell.
This slave cell fires the strobe when it sees a flash from another flashgun/strobe, so it can be triggered by the built-in flash of your DSLR. This is how the picture was made.
I had the DSLR flash set to manual and 1/125th power, and the Sb-26 set to manual and 1/16th power. I then held the strobe in my left hand and the camera in my right. you could use a tripod or light stand for the flash.
the camera was on manual 1/200sec f45 300mm lens at 2foot 0.5meters from subject.
These are not the best shots ever but taken just to show how this works for this brief article.

Shot 1 lit with the camera in-built flash.

From 2009 02 27

OK but very flat.
Shot 2 strobe off camera.

From 2009 02 27

Better I think and more DoF, so sharper front to back.
Like I said not the best shots but I made these while sitting a my desk at work reading my emails, and start to finish 5 mins.