We usually just toss the seeds on the ground from our plants, but nothing has ever grown from that. How exactly do you grow gebera daisies from a seed?

Make certain the seeds you collect, are actually viable ( assuming you aren't sowing a commercial packet) & be certain not to be overly generous with watering, as they may just tend to rot, instead. Use a free draining seed start mix & add perlite if needed. Keep warm & wait about a week to ten days for germination.

How can you tell if the seeds are viable?

If they appear more like a Dandelion seed & blow away, they are likely duds. The viable ones have an obvious thickness where they were attached to the flower stem, when ripe. Not much shrinkage, after drying, of the viable seeds..
I've crossed 'Cartwheel' series before ( 'Strawberry') previously & would pollinate repeatedly, only creating a few viable seeds, from each flower.
There are some good quality macro shots, I've seen, & that may help you distinguish between the stamens (which produce the pollen) & the stygma appearances, to help figure out what you need to do, to transfer pollen, with use of a water color paint brush ( natural bristles.) in your attempt to pollinate & create seeds, between flowers, on different plants.

Goodluck!

I buy seeds for gerbera, and I usually have very poor success. Sometimes germination is alright, but then I lose some in infancy. Last year I started 10 seeds and 2 germinated, of which one died. Don't do what I do.

@Rubi. You have to be careful, not to over water Gerbera seedlings. Otherwise, they may just rot & may do so, before germination, by watering too much. About all they need usually, is just a light misting, from a water bottle. Then maybe you'd have better results.