Marilyn,
You have the Canon 5D, correct? You'll need an electronic cable
release for it. Two from Canon are the Canon Remote Switch RS-80N3 or the Timer
Remote Controller TC-80N3. The former is a simple switch which
replicates the shutter button functions at the end of a 2.5 foot wire.
The latter is a more sophisticated device which allows you to do a
number of additional things with a wired remote for a few more
dollars. I've made do with the simpler one but often wish I had sprung
for the one with greater functionality. If cost is an object there are
also plans to be found online for making your own. The problem with
these is finding the right connector for plugging into the camera.
I swallowed hard and bought the TC-80N3 and have not used all of its
features but those I have used have made the decision to buy it seem
like a good choice. 