use of Have+had+noun.

Please help me to sought out this difficulty:

" they have had to postpone the meeting".

“I have had my post graduate degree from Cambridge University”. :?

“Rachael has had a bad cold for last two days”. :?

In which sort of circumstances do we use this pattern " have/has+had+noun :?:

Which tense does these sentences indicate? please clearify this topic full well and please correct me also if I use incorrect tense or any other grammatical rule in the written post.

I shall be highly thankful to your attention.

hello ESL trainers,
knock knock. . .
If there is any one plz solve my grammatical difficulty. . . I have got a test on monday. Million thanks in advance.