Shuffle Power

Yes, the computer must be ON when you connect the shuffle. It's not the USB cable that requires power. It's the shuffle connected to the USB cable. If the computer is not turned ON, the USB port has no power.

According the iPod shuffle user guide

https://www.apple.com/support/ipodshuffle/ (page 7)

"The battery is 80-percent charged in about two hours and fully charged in about three hours."

More general info about the 4th gen iPod shuffle

https://www.apple.com/ipod-shuffle/specs/

http://www.everymac.com/systems/apple/ipod/specs/ipod-4th-generation-shuffle-4g- mid-2015-specs.html

Power point thing? Do you mean a USB power adapter? Probably the same either way.

Don't worry about it... The first time you use it, you should leave it connected for more than three hours, to give it a full charge. After that, you can connect it to charge whenever it is convenient. You can disconnect it to use, even if it's not fully charged,