“An” at the end of a sentence

I have just seen these sentences and was wondering why “an” is added to the end of the sentence. Further, do you have some guidance to when it should be applied.

“Wann kommt der Flugzeug an = When does the plane arrive”

“Wir fragen sofort an” = We start immediately”

“Wann kommt er an” = When does it arrive/land”

“Welcher Religion gehörst du an = What religion do you belong to”
 

See my answer for einnehmen.
You probably meant “Wir fangen sofort an” = We start immediately”