If my mother died yesterday and I'am the executor of the Will and sole heir, what do I do next?

I am sorry for your loss.  The first thing to do is take care of your mother's funeral and burial, yourself, and your family.  When that is complete, begin looking for and at your mother's assets.

Some of your mother's assets may pass outside the will.  These would include insurance policies with beneficiaries, retirement funds with beneficiaries, bank or investment accounts with joint names, bank or investment accounts with pay on death (POD) or transfer on death (TOD) designations, and some deeds (if in the name of joint owners or life estates with remaindermen).  These assets now belong to the joint owner(s) or beneficiaries and can be settled by contacting the companies or institutions.

You should also begin to gather your mother's bills and debts.  At this point, you do not know what assets will be available in her estate to pay them, but you should start gathering them together so that you will know what is owed.  You are not responsible for paying these bills, so don't pay them out of your funds.

Once you determine the assets that pass outside the will, you can identify the assets that must be included in your mother's estate.  If there are no assets, you do not have to open an estate.  If there are few assets, you may be eligible for a type of summary or expedited administration of your mother's estate.

When you have a sense of all your mother's assets and her debts, I suggest you consult with an estate attorney in your mother's area.  If it will be necessary to open an estate, you will have to hire an attorney to handle that for you.  If you need not open an estate, an attorney can certainly help you wind up your mother's affairs and advise you on handling her assets and debts.

I hope this answer has been helpful.  Again, please accept my condolences.