HE IS TEACHING AND HE HAS BEEN TEACHING

First one HE IS TEACHING this is present continuous tense it expresses that action which is going on in the present.

Ex: I am learning English.
She is dancing.
We are going to Bengaluru.

Second one HE HAS BEEN TEACHING this is present perfect continuous tense it expresses that an action which is started in the past and still it continues in the present.

Ex: I have been learning English.
She has been dancing.
We have been travelling to Delhi.