If I understand correctly you want to tie your own leaders at home and fasten them to the fly line with a loop. Here is how to go about that.
First you need to know that the leader is made up of three basic parts. The butt, the body and the tippet. The butt fastens to the fly line and the tippet fastens to the fly. The body will be made up of more than one piece of leader material. Here is a link
that gives you formulas for tying your own leaders. It will be much easier to follow one of these formulas rather than trying to make you own formula. It is very important that you pay attention to the diameter of the leader sections in the chart.
To prepare the fly line to connect your leader, you need to add a short section of leader material to the end of the fly line. The diameter of this leader material needs to be a few thousands larger than the diameter of your leader butt. For a 6wt fly line and smaller, a .023 to .025 size of leader material will work fine. Tie a short section of the .025 leader material to the fly line using a nail knot. Then tie a perfection loop into the .025 line so the leader material is about 6" long.
So you now have your fly line with a 6" section of .025 on the end with a perfection loop in the end. You now have a loop on the fly line that you can loop on your home made leaders.
I think the above should get you started. If you are serious about tyeing your own leaders you need to buy one of the kits that include all of the leader material you need to tie leaders.
Dan, being a beginner I think you would be much better off buying the knotless tapered leaders. It eliminates a lot of problems you might have with tyeing your own leaders. With a knotless tapered leader you can cut off the first 20" and tie a perfection loop in the end of the shorten leader. If you started with a leader that has a 5X tippet you can take 5X tippet material and loop it to the end of the shorten leader. As you break off flies or tie on new flies you will start using up the tippet you looped on. All you have to do is remove the shorten tippet and replace it by looping on new 5X tippet material. Make you loops as small as you can tie with ease. One knotless tapered leader will last a long time used in this manner.