Sony Xperia Z3+ is an amazing phone but you can make it even better by flashing custom firmware. To do that you will require a custom recovery for Xperia Z3+ such as TWRP. After flashing TWRP on Xperia Z3+, you will be able to do all sorts of hacks onto it including the ability to flash custom ROMs. Here is how you download and install TWRP on Xperia Z3+.
Sony Xperia Z3+ TWRP flashing instructions
This recovery image is for the E6553 single SIM Z3+. Do not use it on another model.
This recovery image requires an unlocked bootloader. You will lose some functionality on your phone if you unlock your bootloader
Do your research and make sure you’re using the latest version of the relevant tools if you do decide to unlock.
This recovery image CANNOT be flashed to your phone. Sony has not yet released the open devices bootloader for the Z3+
Until Sony releases an open bootloader you need to use this image via fastboot boot mode.
Unzip the recovery.zip file to extract the recovery.img file
C:\>adb reboot bootloader
C:\>fastboot boot recovery.img