-te iru and -ing
Alright, so as we've gone through a wide variety of sentence construction, you're probably wondering how to say 'verb-ing' in Japanese. You know, the -ing verbs such as running, jumping, reading, reading, listening. All 'ing' verbs. All of these verbs are in a current state of action.
Base て＋いる is a grammar point that means to be verbing or to be in a state of action. This grammar principle is predicated on combining the Base Te for which can be used for continuation of action. いる which is one of the existence verbs. Combined that relay the continuation or state of the modified verb.
However, watch out for the conjugation with base て since it can vary with different verb endings – like the Japanese verb for reading, yomu, which conjugates in base て form to yonde, which makes the base て＋いる yondeiru.
* When using a movement verb like いく、くる etc. Base て＋いる implies that they have gone and are still there.