Leadcore is definately not the best material in inexperienced hands although I thought these leaders were near to idiotproof as you'll ever get.
The swivel is already locked in the lead clip so all you have to do is pull off the sleeve add your lead and reapply the sleeve.Make sure the lead will discharge with a minimal amount of pressure,the sleeve should come off releasing the lead,try using saliva to lubricate the sleeve before reapplying it.You only want to release the lead should you get a fish take you into weed or thick pads not playing them in open water.
The biggest mistake is that people jam the sleeve on too hard and the fish doesn't stand a hope in hell of discharging the lead,making it pointless using one.
If you're still unsure or in any doubt go to your local tackle shop who
will demonstrate how to use lead clips safely much better than I can instruct over PC screen