This tense is formed with the modal "HAVE" or "HAS" (for third-person singular subjects) plus "BEEN," plus the present participle of the verb (with an -ing ending): "I have been working in the garden all morning. George has been painting that house for as long as I can remember."
Authority for this section: A University Grammar of English by Randolph Quirk and Sidney Greenbaum. Longman Group: Essex, England. 1993. Used with permission.
Generally, progressive forms occur only with what are called dynamic verbs and not with stative verbs. If you wish to review that concept now, click