How does a toilet flapper work?

I'm pretty handy, but when I replace a toilet tank kit, I can't seem to figure out how to not make people have to hold down the handle for the entire flush. What am I missing here?

Under normal circumstances the modern toilet only uses about 1 1/2 gallons of water to flush. That's actually all that's needed for it just being peed in.
For the "other" you need to hold down the handle for the bigger flush.
It's the way they're designed so they're water friendly. The only thing I can think of is to shorten the chain from the arm to the flapper so that it pulls it up higher when it's flushed.

you may need to tighten the chain between the flapper and the handle.

There are many different styles around today.
So you have to be sure you got the right kit.
The basic flapper has a float built into it.
So once the chain is pulled it stays up.
It will only close when the water runs out.
Then the weight of water keeps it shut.
Make sure you didn't reverse it.

the flapper is the eay bit ,it has some little studs on it ,either side of the black part ,cut them off, to suit it ,
it works by pressure of the water pushing down on it , if it too high ,it wont work ,
one more thing place a brick i n there you use less water

Yep, your missing the fact that there is a short flush and a long flush on purpose. But, as the tanks are getting smaller, the long flush often leaves floaters behind.
Where I live, every house is on a water meter. Flushing after a pee is not always needed, you pay for it!
"If it's yellow let it mellow, if it's brown flush it down"
Or, if houses could be designed properly, then water from the basin and bath/ shower could be stored for flushing the pan.
It's a funny old world when we use 2 gallons of prime clean filtrered water to remove a log.

thats what happens when you eat a lot of beans before you go to bed and go to the toilet the next morning...lol

bubble of air under flapper floats it above water when flushed. maybe the flapper is not lifted up enough when flushed or not enought water in the tank.