In The Hunger Games, when or how did Katniss and Peeta meet if they are in diffrent districts?

Unfortunately, I think you have become slightly confused.
If you read the book carefully, it is clear that Peeta and Katniss are actually from the
same district, District 12. If you re-read chapter two, for example, you will see that
both of them are selected to be tributes to represent their district in the Hunger
Games. Therefore Peeta comes from precisely the same district that Katniss comes from.
Also, following Peeta's selection, you will note the way that Katniss feels bad because
she remembers how nice Peeta was to her just after her father's death when she was
struggling to survive and get enough food for her mother and sister. From what we can
understand of this first book, the Districts are very self-contained, and it is
suggested that those within them are not actually allowed to travel to other districts.
This indicates that Peeta and Katniss grew up together in the same
District.