You serve as trustee of your own assets. Then, when you die, they pass directly to your beneficiaries without a probate. Income taxes are due on income you earn. Estate taxes are paid on the net value of your estate as it passes to your beneficiaries. They are in addition to any income tax due.
Estate taxes can be very high, but apply after a relatively high personal exemption.
Much estate planning is designed to minimize these confiscatory taxes. There is no law against it. A few states permit handwritten wills. Most do not. Regardless, the requirements of wills are very technical and vary quite dramatically from state to state.