I'm not a trumpet player, but I do teach trombone and know lots of trumpet players.
You've really gone about this back to front. To get started on a brass instrument, you really need a few lessons. A teacher would lend you or help you find a suitable instrument to buy or rent.
Your Amati should be playable and OK to get started on, if it's all working and set-up correctly. I generally recommend Yamaha student instruments. Not the cheapest, but robust and very consistent - every Yamaha's a good 'un (there are Friday afternoon Kings, Conns and Bachs, and they're always being sold because no-one wants 'em. A Yamaha 1335 trumpet second-hand goes for £150 - £200. Serious players play £1000+ instruments).
Still, now you have a horn, do all the valves work? Are they put in the right casings? (This is crucial - it won't play if they aren't! They're often stamped 1, 2 and 3 on the pistons. If they aren't, never take them all out at the same time because there are an awful lot of wrong combinations of piston and casing and only one right one...) Do the valves work freely and quickly? Do all four tuning slides work? Does the water key leak?
If the trumpet fails on any of these points, find a good brass instrument repairer (ask a teacher, or any trumpet player you see gigging. The best repairers work in spare room and garden sheds, not in music shops, and get their work by reputation among players).
If you don't have any valve oil, get some. "Blue Juice" is the current favourite; you can get it in any decent music shop. Use it as per the instructions.
The price of your horn will buy you two or three lessons. If you're at all serious about learning to play, it's well worth it. Really. Lots of people spend far too much on kit and nowhere near enough on lessons. And it takes lots and lots of practice. No, waaaaay more than that. There will never be a time when you don't need to practice (JJ Johnson).
Another approach might be to find a local brass band - even the famous ones have training bands attached, and if they think you're serious, they may give you lessons cheap or for free - although you'll have to switch to cornet for that.