The present continuous verb tense (or present progressive) connotes an action that is ongoing/has not been completed.
They are eating lunch is an example of a sentence using this verb tense.
In Japanese, verbs are conjugated to the present continuous with the pattern て-form + いる.
The verb いる as you may recall means to be (for living things).
You will find that the present continuous is often used in situations in Japanese where it would not be used in English and vice-versa.
One of the most common examples of this is with the verb 知る, which means to know.
When making sentences like I know the answer or What do you know about computers?, you would normally use the present continuous.
The sentences below are examples of how to use the present continuous.
It is raining today.
今日は雨が降っています。 kyou ha ame ga hutte imasu.
I am reading a magazine.
私は雑誌を読んでいます。 watasi ha zassi wo yonde imasu.
Jon was learning Karate in Japan
ジョンは日本で空手を習っていました。 zyon ha nihon de karate wo naratte imasita.