How do I fix my stupid toilet?

I know I’m just perpetuating the stereotype about women and basic home repair, but whatever.

The chain broke off my lever… though I’m not sure if it’s the lever that broke or the chain, so to be on the safe side, I bought both.

Now, there was only one chain there. It has a rod on it that supposedly attaches to the flapper… but I know mine at home doesn’t have a rod. Is this going to work, or am I going to have to get a new flapper to fit the stupid rod thingie?

And also, I know how to drain the water out of the tank/bowl, but how do I keep it from filling again? Is that the little handle/knob thing on the floor?

feels really stupid