Grammar · Particles
は, the topic marker
[Topic] は [comment]
は marks what the sentence is about, and it is said 'wa', never 'ha'. English has no equivalent, so think of it as 'as for'. Everything after は is the comment on that topic.
The mistake to avoid
It is not the subject marker. That is が, and the difference is the single hardest thing at this level. See the next two entries.
Examples
私は学生です。
わたしは がくせいです。
I am a student.
これは水です。
これは みずです。
This is water.