Buenas he comprado el papel de Yorki por 50.000 de dinero pero no se que hacer después de comprarlo.

Si alguien sabe decirme que hacer se lo agradecería.

Dear @Marcosdm1771996, 

 

After talking to Yorkie's brother and paying him 50K, you can go back and talk to Yorkie on Route 17. 

He will ask you to find a Noctunal Feather for him. You can get it from wild Pidgeotto on Route 16 during Morning and Night.
Upon submit the Noctunal feather, he will give you HM02-Fly, then talk to the manager in Saffron Train station to unlock subway.

 

As @Caelestya has already mentioned earlier here, or you can read more from here: Subway Guide.

 

You can access subway from most PokeCenters in Kanto and Johto with the fee of 2.5K PokeDollar per transport.

If you travel a lot, you can buy train pass from NPC Ticket seller (NPC in department store sells 30 Days Pass cheaper than NPC in Train Station)

Quote

NPC Ticket seller in any Department stores:

   - Small Train Ticket is 15 Days Pass.

   - Big Train Ticket is 30 Days Pass.

 

NPC Ticket seller in Train station (Saffron city and Goldenrod city😞

 

If you have further question, feel free to ask.

 

Best regards, 
PinkFurret