# When they came

The word "they" refers to the participants in the burial procession.

# floor of Atad

Possible meanings are 1) the word "Atad" means "thorn" and it may refer to a place where large amounts of thorns grew, or 2) it may be the name of the person who owns the threshing floor.

# they mourned with very great and grievous sorrow

"they were extremely sad and they mourned very much"