Subject / Object:
Every sentence has a subject and a verb. The subject is a noun (name of an object/person/place). The subject is usually the first noun in the sentence (if there is more than one) and the subject does the verb, e.g.
The cat is eating tuna.
In this sentence the cat is the subject as it is doing the verb (eating).
Some sentences have a object which is also a noun. The object of a sentence has the verb done to it. in the above sentence, he tuna is the object as it is being eaten.
Active / Passive:
Active is when the subject does the verb to the noun, e.g. The cat (subject) is eating (verb) the tuna (object)
Passive is reversed in that the subject has the verb done to it by the object, e.g. The tuna (now the subject as it comes first) was eaten (passive verb form) by the cat (object)
Often people think of verbs as ‘doing’ words. This is true for the majority of verbs but not all verbs. it is more accurate to think of verbs as words that have different tenses (past, present, future), e.g.
Is is not a ‘doing’ word. However, it has a past tense (was) and future tense (will be).
This web-site gives a good explanation on what parenthesis is and how to use it.