idb is made up of 2 parts, each of which needs to be installed separately.
Each target (simulator/device) will have a companion process attached allowing idb to communicate remotely.
The idb companion can be installed via brew or built from source
brew tap facebook/fbbrew install idb-companion
Note: Instructions on how to install brew can be found here
A cli tool and python client is provided to interact with idb.
It can be installed via pip:
pip3.6 install fb-idb
Note: The idb client requires python 3.6 or greater to be installed.
Note: Instructions on how to install pip can be found here
Make sure both parts of idb are installed successfully and then you're good to go! Head over to the guided tour to try idb out.