This particle は(wa) is used to show what one is talking about, or the subject of the sentence.
It can be thought to mean as for or speaking of . . . and represent a topic where the rest of the sentence is some statement about it.
は is read as wa when used as a topic-marking particle, but it is read as ha in all other contexts.
この ほん は あかい です。
(Kono hon wa akai desu)
This book is red or (As for this book, it is red)
わたし は がくせい です。
(watashi wa gakusei desu)
I am a student (As for me, I am a student)