With respect to assets with a beneficiary designation, you contact the company involved and ask what paperwork they need to make a distribution happen. Usually, it is a death certificate and a company specific form that establishes the domicile of the decedent and the identity of the claimant. Often these forms need a "guaranteed signature" which is a bank backed alternative to a notarization.
If there is any real estate or there are significant assets, an intestate probate estate is opened and the next of kin with priority under the relevant statute is appointed as executor and distributes the remaining property in accordance with the laws of intestate succession.
If there is only tangible personal property and a small amount of financial assets that have no beneficiary or joint owner, it is sometimes possible to collect and distribute those assets by affidavit or in a streamlined small estates procedure.
Either of the latter two situations really call for a lawyer to be involved.