What/how do I declare things for US border customs and do I keep them in a carry on or in checked baggage?

I've looked online and also here on reddit, but a lot of Info here is a bit older and I'm a bit anxious about doing everything right.

I've downloaded the CBP form to fill out, and they say onlike I should declare everything, even if it's allowed stuff, and that it's better to overdeclare.

I have some candy/chocolate (below 100US$), some prescription drugs (with an extra form filled out by my doctor) and a few relatively cheap presents, maybe around 30€. So if I'm putting all of that down, I then have to go in the lane where I can declare stuff? (Are there still separate lanes for that? It's been ages since I've so much as been at an airport...)

And since I declare all this, do I need to put it into my carry on bag so they can check everytjing if they want, or can I just pack it into my checekd baggage?

Also, in case it's relevant, I'll be traveling through Dublin, and go through customs there as far as I'm aware.

Thanks for your help!