Here is a quick walk through of the the 3 ways to install an Arduino library. If the library is a part of the Arduino system it will show up in the library manager, otherwise it must be downloaded and installed via .ZIP or manually.
Please note starting in 2024 we are using Arduino IDE2.2.X . The interface looks different than below (IDE 1.X), but the basics are the same.
The instructions for library installs in Arduino IDE2.o can be found here: https://docs.arduino.cc/software/ide-v2/tutorials/ide-v2-installing-a-library/
This video summaries and reviews the Arduino post on library installation for IDE 1.x.