Once i paint on tiles from a tileset how do i give those tiles physics (ex. box collider)

I imported a

I was following a course on youtube by brackeys and it showed how to use tilesets for the ground. But everytime i play the game the character just falls right through the ground. So this brings me to my point asking how to add physics to a whole tileset.

You can attach a TilemapCollider2D component to the tilemap, which will generate the collision shape. See this documentation.