When Krypton is on the verge of destruction, Jor-El and Lara Lor-Van send their children Kal-El and Bar-El to the planet earth. Along with them, comes their cousin, Kara Zor-El. Kal-El safely gets off the atmosphere but the destruction of Krypton sends a wave towards Bar's and Kara's pod and they get stuck in the Phantom Zone, a region in space where time doesn't pass.
11 years later, Bar-El's pod escapes the Phantom Zone and arrives at Earth, near the house of Henry and Nora Allen.
(This story is not for West-Allen fans. It is for Snowbarry fans.)
(I, obviously, don't own any characters from Arrowverse.)