To code I used Android Studio (click here to download). You will need Java installed on your PC, and I advise you to follow the steps described on this page. I consider that you have a PC running on Windows, if it’s not the case, either you code without Android Studio (AS) (not hard to do, just a bit longer) or you lay find a way to install it anyway on your computer. To familiarize with android studio (at the beginning of the projects, I was probably newbier than you at android programming), I followed those two tutorials:
Those two links are not mandatory at all to code on android, they will just make your work faster if you didn’t know about android programming before.
Finally, to test your app, you have two options, the emulator and a real phone. The advantage of the real phone is that’s it’s easier to use the network (Wi-Fi, Bluetooth, etc…) with it, for example, the local ip (localhost) for the emulator is an alias: 10.0.2.2. But the emulator is still a good option if you don’t have anything else.