This tense expresses an action that started at some point in past and has continued to the present time. It states an ongoing nature of an action that started in past and is still continued in the present. Therefore, a time-reference is given in the sentence to show when the action started in past or for how long the action is being continued. This time-reference distinguishes present perfect continuous tense from ordinary present continuous tense where the time of continuity of action is generally not specified. 

The specific words ‘since’ and ‘for' are used in the sentence to show the time of action.

• If the exact starting time of the action (e.g., Monday, 3 P.M) is known, the word ‘since’ is used before the time in the sentence.
• If the exact starting time of an action is not known but only the duration of time for which the action is being continued (e.g., three hours, five months, four years) is known, the word ‘for’ is used.

Main verb: 1st form of verb + ing, (Present participle) e.g., eating, buying, going.
Helping verb: Has been / Have been.

If the subject of the sentence is ‘he, she, it, or a singular noun’, then ‘has been’ is used.
If the subject is ‘I, we, you, they or a plural noun’, then ‘have been’ is used.

 Subject + helping verb + main verb + since/for + time
 Subject + has been/have been + (1st form of verb+ing) + since/for + time

Examples:

In negative sentence, the word ‘not’ is added inside the helping verb making it as ‘has not been’ or ‘have not been’.

 Subject + helping verb + not + main verb + since / for + time
 Subject + has/have + not + been + (1st form of verb+ing) + since/for + time

Examples:

The question sentence starts with ‘has’ or ‘have’ and the word ‘been’ comes after the subject inside the sentence.

 Has/have + subject + been + (1st form of verb+ing) + since/for + time

Examples: