I'm not a lawyer, but here's my understanding of how the Fifth Amendment works:

It guarantees that you can't be compelled to give information that will then be presented as evidence against you when you are being prosecuted for a crime. It doesn't give you the right to refuse to give information in general.

For example, you can't refuse to give information just because it might be used against you in a CIVIL lawsuit. Or because your boss might fire you if he knew. Or because other people might be prosecuted. Or because people might throw rocks at your kids.

Once you refuse to give information, and cite the Fifth Amendment as your reason, the government then has the option of granting you immunity from prosecution. A grant of immunity is simply a binding promise by a prosecutor (or in the case of testimony before a congressional committee, by Congress itself) not to use the information against you. (A promise by Congress would be binding on federal prosecutors as well.) Once you have that promise, and there is no possibility you will be prosecuted, the Fifth Amendment no longer gives you any protection. You can then be compelled to testify, and imprisoned if you refuse.

I've never seen an actual grant of immunity, but they must be complicated, carefully worded documents. The government has to spell out what kind of information they won't use, without necessarily knowing what kind of information you have to give. And they don't want to give away the store, either.

There are such things as limited grants of immunity, and, I think, conditional grants of immunity. They might grant you immunity from being prosecuted for murder, for example, but not for kidnapping. Or for the murder of one particular person, but not for murder in general (in case you murdered someone else).

There are gray areas. For example, is a promise by a federal prosecutor binding on a state prosecutor? I understand the general answer is no, but state prosecutors usually voluntarily honor federal grants of immunity, as well as those of other states.

Kenneth Starr, a federal prosecutor, gave immunity to Linda Tripp before she handed over the tapes she had illicitly made of phone conversations with Monica Lewinsky. Of course, Tripp WANTED to testify, and Starr had no desire or reason to prosecute her, but she wanted immunity anyway, because she had violated a STATE law in Maryland by making the tapes. After the impeachment trial was over, the Maryland attorney general wanted to prosecute her. A federal appeals court ruled that Tripp could be convicted only if the prosecutor could prove his case without using any of the evidence that Tripp had given to Starr. In other words, he would have to have an independent source of evidence. The prosecutor decided he couldn't meet the burden of proof, so he dropped the charge.