Sorry about your loss. If your son had a will, then the will governs who should receive what. Hire a probate lawyer in your area to help you review, understand and administer the will. Likely if your son was young (you didn't indicate) his estate should be relatively simple so a consult with a probate attorney may be all you need to handle the estate. You might be able to take the lawyers guidance and do the rest on your own (but see below).

If your son did not have a will (he would be said to have died intestate) you need to look at the laws of intestacy in your state and see what they mandate for how assets are distributed when someone dies without a will. Likely, most or all will be distributed to the parents (you) since your son was not married and had no children. Intestacy is usually a bit more complicated so you might need a bit more help from a local probate lawyer (but see below). Someone (perhaps you) has to be appointed to manage the estate. When there is no will this person is often called the Administrator. Your state laws (you can probably find them on line at your state website or at your local library) will specify which relationship of person is to be appointed.

Before you proceed, two other points. Many probate or surrogate courts have special simplified proceedings for very small estates. Look up on line or in the Yellow Pages the local court that handles wills and probate. Call them and ask about such a proceeding. If they have one, and your son's estate is small enough, you might be able to handle it there cheaper and more quickly.

Finally, joint bank accounts, IRAs and insurance with beneficiary designations are paid to the joint owner or the beneficiary. For may young people there is nothing to probate. So first review the assets your son had to see if any of these apply.

Sorry again about your loss. You might consider making a charitable gift in memory of your son, a gesture many find gives them some solace in such a tough time.