Hello, JVC, & welcome to the NAFC Forums. And if you've recently joined the North American Fishing Club, welcome to the Club as well.
First of all, do you have the right size of tube jig? Inserting one that's way too big for the tube just ain't happening. Make sure it'll fit in there in the first place. If you have doubts, ask the guy at your local tackle store what size to use for the size tube you'll be fishing with.
To insert a standard tube jig into a tube (one without a weed guard), slide it into the tube from the back, by all of those little legs. The way to get a tube jig into a tube is s-l-o-w. Take your time, and gently insert the jig into the tube, but first make sure there are no sharp edges or protusions on the jighead that may have been left after the thing was made at the factory. If there are, scrape them off with your pocket knife and make the jighead smooth, so it won't dig into the inner walls of the tube. If the jig's tie-on loop is close to the front of the jighead, insert the loop first and stretch the tube over the blunt smooth lead, rather than inserting the lead first & then trying to stretch it over the much narrower, sharper tie-on loop. If the loop is more toward the center of the jighead, though... well, you won't have much choice but to tuck the lead in first... just do the best you can sliding it on. You may have to lubricate. If you're going to use a scent attractor, that stuff will work just fine as a lubricant. Squirt some on the jig before trying to pull the tube over it. If you're not going to use scent, dip the jig into the water & get it wet, then try inserting it (again, doing it slowly... you're rigging a tube bait, not putting out a fire, so taking your time is OK). Also, don't pull the tube over the jighead by the small legs at the back. Try grabbing the body & sliding it over the jig kind-of like you're sliding a radiator hose onto a radiator or thermostat housing on a car. If you want the tube to act like a regular jig, slide the weight as far forward as you can into the tube's nose. If you want the tube to spiral as it falls, leave a little gap between the nose of the tube & the front of the jighead. When you have it in position, push the tie-on loop right through the plastic wall of the tube, then tie it on & fish.
You can thread the tube on a ball-headed jig as well, just like you'd thread a Mister Twister or any other soft plastic on one, leaving the jighead outside the body. But to keep the lure as snag-free as possible, use a tube jig & hide it in the tube.
And, if you want to Carolina Rig or Texas Rig the tube, follow the good advice Goinfshn provided on putting them on the hook.
Hope I helped. And, again, welcome. Good to have you here.
If I'm not fishing, I'm thinking about it. Keep the line fresh, the hooks sharp, and have fun fishing. God bless you. -Sonny, Life Member since 2002