を vs. が

Have you ever noticed that both the particle Wo and the particle Ga are used before a verb?

This is because depending on the type of action and verb, a different particle must be used.

Let's remember that the particle Wo always takes a subject, and has a common structure of:

Subject は / が Object を Verb

NOTE: Let's remember that the subject can be omitted to avoid redundancy, so we might end up seeing just a sentence with "Object を Verb"

The type of verbs that carry the particle を are called "TRANSITIVE" verbs. 

That is because: there is a transfer of an action from the subject to the object.

Or how we would know it in Japanese 他動詞「たどうし」A verb done to other things

Good examples that use the particle Wo are the verbs "To Eat" and "To drink"

(わたし　は　）すし　を　たべる

Watashi wa sushi o taberu

(I) eat sushi

(わたし　は)　みず　を　のむ

(watashi wa) mizu wo nomu

I drink water

Now, let's talk about the particle "Ga"! Well... Easy, there's NO OBJECT! And this happens in pretty much two case scenarios:

1) The object becomes the subject, who then performs the action by itself (The light turned itself off -- maybe because the bulb burn out?)

2) The action was previously performed (The light is off... maybe somebody turned it off a few minutes ago, yet that doesn't really matter)

Now, as opposite from being transitive is "INTRANSITIVE" verbs! and these can be taken by particles such as the "Ga" particle.

Or how we would know it in Japanese 自動詞「じどうし」A verb done by itself

SOOOO, what is the biggest problem with these two particles? The main issue is that the verb changes (most of the times) depending if your sentences is transitive (wo particle) or intransitive (ga particle). For example

 (私　は）まど　を　あけます = I open the window

まど　が　あきます = The window is open

In this example, the verb "To Open" is

あけます (formal) or 　あける (informal) if the sentence is transitive = open something

あきます (formal) or あく (informal) if the sentence is intransitive = something opens

Now let's take a look at a couple more examples,

(私は)　まど　を　しめす　＝　I close the window

まど　が　しまります　＝ The window is closed 

(私は)　でんき　を　けします　= I turn off the power

でんき　が　きえます = The power is off

(私は)　でんき　を　つけます = I turn on the power

でんき　が　つきます = The power is on

(私は)　でんわ　を　かけます　＝　I make a phone call

でんわ　が　かかります　＝　The phone rings

(私は)　ほん　を　ならべます　＝　I line up the book

ほん　が　ならびます = The book is linking up

(私は)　くるま　を　とめます　= I park the car

くるま　が　とまります = The car is parked

I hope these examples gave you a better idea of the difference between Wo and Ga.

This "Transitive" and "intransitive" verbs topic can get very complex, but this post is just meant to give you a brief idea of the difference. This is a topic that is mentioned to beginners of the languages, so a very important one to start practicing.

Now the question is, Is there an easy way to remember the difference between Transitive verbs and intransitive verbs? Unfortunately there's no easy "hack". The best way to learn them is by pairs and in context (that is in actual sentences).