Here are just a few differences:

Bitcoins are an electronic form of money.  Dollars are a physical form of money made of linen.

Bitcoins are limited in quantity.  The Federal Reserve can create as many dollars as they want.

You can create a backup of your access to bitcoins.  You can't create a backup of your dollars.

You can secure your access to your bitcoins with a password and cryptography.  You can't encrypt your dollars.

It is much easier to store a large amount of bitcoins.  It can be difficult to securely store a large amount of dollars.

You can send bitcoins over the internet.  It is difficult and/or expensive to send dollars over significant distances.