Route 22 is a very short route west of Viridian City. There are some new Pokemon in this area that can be useful to the upcoming Gym battle. Try capturing a Nidoran ♂ or a Mankey. Their fighting attacks will be very useful at the Gym.
To the north of the tall grass is your Rival. He will challenge you to another Pokemon battle. This time he will have two Pokemon. Do not try to fight him unless you have several Pokemon that are at a high enough level. Again, this battle may determine what your Rival’s Eevee evolves into later in the game.