Jeff H has his sling set up correctly, with one exception -- the spring clip should be on the buttstock end instead of on the forward swivel.
If you compare the old M1907 leather sling with the M1 web sling that replaced it, you'll understand why. The rear loop on the M1907 sling could be tightened around the shooter's upper left arm (if he was right handed) to steady the rifle in deliberate shooting. The standing loop on the M1 sling can fulfill the same function, but to do that, it must be detached from the butt swivel. The spring clip provides a convenient way to do that.
I think that slings-as-shooting-aids are pretty much obsolete. Nowadays, they're simply carrying straps.