Many Japanese learners tend to be confused with using the は and the が particle. As previously mention, the は particle is use for introducing new information to the listener, like a topic marker. The Japanese may also use this to emphasis certain things.
While for the が particle, it is use as a subject marker, or use for certain things that are already known between the speakers and listeners. Let’s take a look at some examples between the は and the が particle.
これ は わたし の ほん です
This is my book.
この ほん は わたし の です
This book is mine.
Before we get into the は explanations, there are some more explanations. この means “this”. The Japanese use この for telling which object to referring to.
For example
この こ -> This child
この パソコン -> This computer
この パン -> This bread
The Japanese don’t say これ ほん, its not correct. Only by saying これ は is correct and this word and particle will always be together. If you want to say “This book”, then say この ほん.
So from the above sentences you can see the は is used for introducing new information or changing topic. これ is new information. この ほん is also new information. But when the Japanese want to talk about the current or previous information regarding certain matters of objects, the Japanese will use the が to mark the subject.
Aさん：これ は わたし の ほん です
This is my book.
Bさん：これ が あなた の ほん です か？
Is this your book?
A introduce new information, telling B that this is his book. And B just learned about book, so he confirms the matter by asking A about the book.
So this is a very clear understanding of how to use は and が. I will cover more information in the future posts. Happy learning Japanese 
