Present Continuous :
-Right now, Sarah is writing the letter. (active )
-Right now, the letter is being written by Sarah. ( passive )
Simple Past :
-Sam repaired the car.
-The car was repaired by Sam.
Past Continuous :
-The salesman was helping the customer when the thief came into the store.
-The customer was being helped by the salesman when the thief came into the store.
Present Perfect :
-Many tourists have visited that castle.
-That castle has been visited by many tourists.
Present Perfect Continuous :
-Recently, John has been doing the work.
-Recently, the work has been being done by John.
Past Perfect :
- George had repaired many cars before he received his mechanic's license.
- Many cars had been repaired by George before he received his mechanic's license.
Past Perfect Continuous :
- Chef Jones had been preparing the restaurant's fantastic dinners for two years before he moved to Paris.
- The restaurant's fantastic dinners had been being prepared by Chef Jones for two years before he moved to Paris.
we often use the continous form when the action takes a lot of time .or when it's happening at the moment .
example : I am driving ( means that I am driving right now at the time of speaking ).
I drive ( it could be anytime ).
past continous is when something happen in the past and didn't end still going or took a lot of time to finish .
perfect tense : we use it in the conditionnal type , when there are to action happening in a sequence , I am not sure about it.
I hope i helped little bit.