ACTIVE SENTENCES
An active sentence is the opposite of a passive sentence.  In an active sentence, the subject performs the action of the verb.

Examples:The dog ate all the biscuits.
(In this example, "the dog" is the subject of the sentence - subject of the verb "to eat", i.e., "The dog" is the thing that did the eating. Therefore, this is an active sentence.  Compare this to its passive version: "The biscuits were eaten by the dog." In this example, the biscuits did not perform the action of the verb. In fact, it was done to them.  Therefore, it is a passive sentence.)
Tony is trimming the hedges all week.
("Tony" - active subject, i.e., doing the action (trimming))
Hammerhead sharks will pester you as you approach the reef.
("Hammerhead sharks" - active subject, i.e., doing the action (pester))

PASSIVE SENTENCES
In a passive sentence, the subject does not perform the action in the sentence.  In fact, the action is performed on it.

Examples:Anita was driven to the theatre.
(In this example, "Anita" is the subject of the sentence - subject of the verb "was".  However, she did not perform the action of the verb "to drive".  The action was done to her; she was the recipient of the action.)Nowadays, kites are protected.
("kites" - passive subject, i.e., the action is being done to them)The olives are stoned and crushed in this area.
("olives" - passive subject, i.e., the actions are being done to them)

In a passive sentence, the person or thing doing the action is usually preceded by the word "by".

Examples:
Anita was driven to the theatre by Carla.Nowadays, kites are protected by law.The olives are stoned and crushed in this area by my son.