When the lawyer reads my Dad's Will, does everyone have to be there like you see on tv? a

Sorry, I should have asked: are you also your father's executor? Your POA expires when - may he live forever - your father does. It's the executor of his will, which may or may not be you, who is responsible for ensuring that beneficiaries receive their bequests according to your father's instructions, and not according to whether they attend a reading of the will.

Wills are public documents and may be viewed by anyone who knows how to go about requesting sight of them. As far as I know, the reading aloud after the funeral tradition has no basis in law; but it is an extraordinarily handy device for scriptwriters wanting to start a really juicy fight among their lead characters. Are you worrying about having to notify lots of people whose addresses you don't know, or something?

No. They don't.

The Executor is in charge. The heirs named in the Will are usually invited to a reading, if there is one. The Executor puts any money into an "Estate of XXX XXXX" account. He pays all bills against the estate. He sells off the houses, cars etc and puts that money into the Estate account. Then he waits. Here in NY I have to wait 7 months for any bills that might come against the Estate. I have to do a 2014 tax return for the Estate. After March of 2015, the waiting period is up, and I distribute what is left according to the Will.
Some states have longer waiting periods, maybe two years.
Don't expect anything to happen very quickly.

There really can't be a requirement that everyone be present -- sometimes people are left something and they know nothing about it. How would they know to be present at the reading?

You should call the lawyer who prepared the will and ask. Has your dad passed away? If not, why are you asking? Your POA expires when your father dies. Who is executor?