arcpy ships with Esri's ArcGIS software package. It is neither free nor open source and, even if you were able to obtain it without an ArcGIS license, you would not be able to use it as it has a built-in license checker.
If you do have an ArcGIS license, but are trying to use
arcpy in a Python environment other than the Esri default, I would recommend doing so with Anaconda, using a setup like the one described here.
If you don't have an ArcGIS license, there are several free and/or open source alternatives available, which other users here know much more about than I do.