The way to tension an elastic is to thread it in the normal way, attach the the elastic to the bung. Then with a piece of elastic hanging from the tip stretch it so it bottoms out then let the elastic retract back into the pole. Now there should be a bit more elastic hanging out than before so without any tension hold the elastic at the point where it comes out of the tip and pull approx 3" out, this is the point where you will attached you connector or make the crows foot.
An even better way is to have a bung that has a tensioner built in, this way you can wind a bit more elastic onto the bung sorting out any 'droop'. It is also very useful for when the elastic gets a bit warn you can simply remove a few inches and tie on a new connector and release a few turns on the bung.
A 'crow's foot' as I remember is a tied loop with the loop cut off leaving three loose strands of elastic. It's just a bulky knot to stop the elastic slipping back into the top section. The rig is fixed on by creating a loop within a loop along the nylon and pulling it tight.
Difficult to describe, easy to do, but totally useless. Stick to an adapter.
I actually use the crows foot on small elastics, up to an 8, above this I use connectors. I find that it a great way of attaching a rig especially when snatching small fish, there is less ressistance than using a connector. But then again it's just preference.
If you do you the crows foot on small elastics make sure that you tie in a length of say 16 elastic so that the knot does not slip back into the pole!!
No problems Simon, thats what this site is about - if you are not sure about something then somebody else is more than likely too.