How do you catch a Pokemon on Pokemon indigo?

On the top toolbar, rollover, don't click, just rollover Shops, Centre and More. Click on the text that says "PokeShop", and then at the new page, above the items you'll see a small toolbar. Click PokeBalls, and buy some. There are four types, Pokeball, Great ball, Ultra ball and Master ball. Once you're done there, on the top toolbar, click Maps or Rooms, and on the new page, select a map or room. Then, walk around with the keyboard or by clicking the movement pad on the bottom-left of the map. Wait for a Pokemon to show up, then press Fight. Battle the Pokemon. If it's HP gets down to zero, refresh the page and press Retry. (It works, believe it or not!) The Pokemon's HP will still be down at zero, but I won't have fainted yet, making for an easy catch. (You also get double the EXP and money) Click Items, and then press the Poke Ball. There you go! If it didn't work, refresh again and then try with a different Poke Ball type.