I Beleive You Are Talking About HG/SS. Heres How You Get Them:
Kanto Starter Steps:
Step 1: You HAVE To Defeat Red.
Step 2: Go Into Prof. Oaks Lab In Pallet Town
Step 3: Pick A Kanto Starter.
Hoenn Starter Steps:
Step 1: Beat Red
Step 2: Meet Steven Outside The Fanclub In Vermillion City
Step 3: Go into Silph Co. In Saffron City
Step 4: Go Up To Steven And Talk To Him
Step 5: Pick A Green Plate For Treecko, Red for Torchic, and Blue, for Mudkip
Hope This Helps:)