Adjoin means ‘to be next to; to be in contact with’. For example: “Yes, it is true that our house adjoins theirs.”
Adjourn, on the other hand, means ‘to put off or to suspend until a future time’. For example: “The judge adjourned the case till next week”
A 2nd meaning for adjourn is ‘Move, depart for’. For example: “Having finished dinner, they decided to adjourn to the living room.”
Usage example that uses both these words: We decided to adjourn our meetings for the day so we could go for lunch in the restaurant in the building which adjoined our meeting place.