When do we use future perfect continous? I'm a little weak in Tenses...

Future perfect continuous tense:

The actions or events which will be continued over a period of time and will be completed in future are indicated by the future perfect continuous tense.

The sentence structure for future perfect continuous tense:

Subject with 'Will or shall' with the helping verb ‘have’ + been and the Base form of the verb ending in –ing with the Object.

Let us look at this example:

“I will have been waiting for him for two hours.”

The subject of the sentence is ‘I’, 'have' is the helping verb with 'been' added to it, 'waiting' is the main verb ending with ‘-ing’ and ‘him’ is the object of the sentence.