ADB can detect devices but it can't detect device in recovery move I am using mac.
I am trying to install twrp on my Galaxy Note 8.0 GT-Nn5120, via adb. ADB can detect the device when in normal mode but when i boot into recovery mode, it can't detect the device.. What do I do
You can't ADB in recovery mode, not with a stock recovery. You can only ADB Sideload which is used to flash zip packages (updates, gapps, etc). To install TWRP, you need to flash it in Download mode.


Download TRWP or here
Boot in Download mode (Hold volume down then briefly press the power button. Press Volume up to confirm).
Download and unzip Odin then launch it.
Click on PDA or AP button and select TWRP file you downloaded previously (Should be in .tar format. If in zip, unzip it)
Click on Start button 
When you see PASS, disconnect the phone and power on (Hold volume up this time: you should boot in TWRP recovery )