Capital gains are profits realized from the sale of assets; a tax is triggered only when an asset is sold, not held.
Everything you own, whatever the form of ownership, is subject to federal, and possibly state, estate taxes.
The federal gift tax applies to gifts of property or money while the donor is living.
IRAs and employer-sponsored retirement plans are subject to annual contribution limits set by the federal government.
Required minimum distribution is the annual amount that must be withdrawn from a qualified retirement plan/account.