”Be just about to."
Tokoro da is used to express an action which is about to take place. In this usage, tokoro means "state" or "time."
Kuruma wa kado o magaru tokoro desu.
The car is just about to turn the corner.
Akira wa ima neru tokoro da.
Akira is just about to go to bed now.
Densha wa shuppatsu suru tokoro desu.
The train is just about to depart.
Hope this was helpful, and see you next time!
°˖ ✧◝(○ ヮ ○)◜✧˖ °こゆうきあいはら°˖ ✧◝(○ ヮ ○)◜✧˖ °