Hi Paleo, it's great to see someone getting into this hobby at such a young age, there's certainly worse things you could be doing with your time.
In my opinion, the Ace 250 is one of the easiest to learn detectors on the market as well as providing the best value for money. It shouldn't take you long to make back what you spent with this machine.
As always, I suggest thoroughly reading the user manual and watching the DVD that came with it (you'd be surprise at how many people that don't do this), also check out plenty of YouTube videos, and most importantly get out there and book some hours up on your new detector. This is the best way to learn.
I would start by using the predefined search modes while you're getting the hang of things, you can always alter the notch discrimination (for target elimination) to suit your needs once you've learned to differentiate between targets (i.e. coins, bottle tops, nails etc). Listen out for clear signals that sound very similar from left to right, right to left, as these are often quality targets such as coins and jewellery. One way or broken up signals are more likely to be trash.
Detecting in public, yes this can be a little embarrassing at first but don't let it get to you. You could try detecting during non-peak periods until you become more comfortable. And always remember when detecting in public to be mindful of your surroundings and try not to bother anyone.
Have a search around the forum as there's quite a bit of information on the Ace 250.
Nugget.