Once you load the ROM, the emulator will ask for controller setup. You can play with a keyboard, but God help your fingers (and your sanity). Go buy a USB controller for $15 – it’s worth skipping one coffee run. Map the A button to the bottom face button, B to the right one, and Start/Select to the top left buttons. Trust me.
Pro tip: Save states are your best friend. Instead of walking to a Pokemon Center, just hit Shift + F1 to save instantly. Did you just accidentally run from a shiny? Ctrl+Shift+F1 loads your last save. You’re basically cheating, but in the most satisfying way possible.
4 Ways to Play Pokémon on Your PC - wikiHow