There are 3 general cases where the particle を is used.
But first, let's remember that when it is used as a particle を is actually pronounced as "o"
Now, let's take a look at the 3 general cases:
CASE #1:
Particle "wo" is known as the "Object Particle" and that is that it indicates the direct object of a verb.
The common structure is:
SUBJECT は OBJECT を VERB
Example (1):
私 は 本 を 読みます 「ほん を よみます」= I read books
Subject = 私「わたし」I
Object = 本「ほん」Book(s)
Verb = 読みます「よみます」Read
Example (2):
彼 は 寿司 を 食べます 「かれ は すし を たべます」 = He eats sushi
Subject = 彼 「かれ」He
Object = 寿司 「すし」Sushi
Verb = 食べます 「たべます」Eats
NOTE: Sometimes it is easy to confuse particle "Wo" and particle "ga".
The particle "Ga" is used to take on indirect objects (meaning that there's not subject in the sentence)
For example:
わたし は ドア を しめます = I (subject) close (verb) the door (object)
vs.
ドア が しまります = The door (object) closes (verb)
CASE #2:
The particle "wo" is used to indicate a route of a movement or motion. Therefore it is used with verbs that describe motion.
Example (1):
CASE #3:
The particle "wo" is used as a point of departure.
Example (1):
彼女 の 息子 が 家 を 出ること を 悲しむ
「かのじょ の むすこ が いえ を でる こと を かなしむ」
She is sad because her son is leaving home
Example (2):
A「トイレ は どこ です か」
B 「あの緑のドアを出て、右に曲がってください。」
A "Where is the bathroom"
B "Leave from that green door, then turn right"
Example (3):
バス を おりて、５分くらい あるきます 「５分 ＝ ５ふん」
Get off the bus and walk for about 5 minutes
