YOu have to go to the Dance theatre in Ecruteak city, located behind the Pokemon center. There's is a team rocket grunt inside on the stage. YOu have to press "a" on him and challenge him. Once you...
Ekans can be found in the grasses towards the beginning of the game. Mainly, it can be found around Azalea Town. After exiting the cave to get to the entrance of Azalea town, there is a small grass...