Patching a liner isn't all that complicated - you need a piece of new liner large enough to cover the hole and some liner patch adhesive (Boxer 100 is probably the best), a pair of decent scissors, and a wallpaper seam roller to help apply the patch.
For patches on the floor you probably need SCUBA gear since a new patch needs to be worked for a few minutes to insure that it doesn't just peel right off.
To properly apply a patch, cut a piece of new liner material so that it is large enough to cover the tear with ~3/4" overlap and be sure to round off any corners unrounded patches come off fairly easily. Apply a thick, even coat of the adhesive to the back of the patch and fold it in half so that it's glue to glue.
Unfold the patch right at the leak and apply it - this is where you use the seam roller roll the patch from the center out using good pressure on the patch then spend a minute or two rolling around the edge of the patch.
This won't work if there is a crease where the patch needs to go - if you have water behind the liner you should be able to push the creases back to the walls. If you don't have water behind the liner, you can try using a toilet plunger to work out the wrinkles - as a last measure (if your liner has enough elasticity to be able to move the creases you can lower the water in the pool, work out the wrinkles and use a vacuum to hold the wrinkles out while the pool refills. Don't want to try this with an older liner or one that has been chemically abused. There is too much chance of ruining the liner.
It's often impossible to patch the underside of the liner of a in-ground pool. If you can get under the liner, by all means patch the backside too. And put 2 patches if you need to on either side, put the first one on, as per above, and then cut another patch to be ~ 3/4" larger than the first and apply it after the glue has set on the first one, the more protection for the hole in the liner, the better it will stay sealed for the life of the liner.
It's usually better to use a piece of the liner if you have it. It'll come closer to matching the existing liner than a patch probably would. If you're putting it on the back side of the liner it really doesn't matter though.