How do I change default screenshot location in MAC?

To change default screenshot location in MAC just enter this into Terminal: 

defaults write com.apple.screencapture location ~/Documents

killall SystemUIServer

How do I view hidden files on my MAC Finder?

To show hidden files in Finder just enter this into Terminal: 

defaults write com.apple.finder AppleShowAllFiles YES
killall Finder

How do I enable airdrop on my mac?

Enable Airdrop

To add AirDrop to Mac just enter this into Terminal:

defaults write com.apple.NetworkBrowser BrowseAllInterfaces 1

defaults write com.apple.NetworkBrowser DisableAirDrop -boolean NO

killall Finder

Additional Information

AirDrop requires that both Mac computers include Wi-Fi hardware that supports AirDrop mode. Both Mac computers need to have OS X Lion or later installed.

To see if your Mac works with AirDrop, make sure you’re in the Finder by clicking the desktop (the background area of your screen), or by clicking the Finder icon in the Dock. Then, check to see if AirDrop is listed as an option in the Go menu. If you don't see AirDrop listed, your Mac doesn't support this feature.

Macs that include AirDrop support are the same as, or newer than, the models listed below.

    MacBook Pro (Late 2008 or newer)*

    MacBook Air (Late 2010 or newer)

    MacBook (Late 2008 or newer)*

    iMac (Early 2009 or newer)

    Mac Mini (Mid 2010 or newer)

    Mac Pro (Early 2009 with AirPort Extreme card, or Mid 2010)

*The MacBook Pro (17-Inch Late 2008) and the white MacBook (Late 2008) do not support AirDrop.

Please check Apple support site for more information.