The recommended way to install pyrosm is by using conda package manager:
$ conda install -c conda-forge pyrosm
Pyrosm is also distributed via PyPi and it can be installed with pip:
$ pip install pyrosm
Pyrosm has a few dependencies (Geopandas, Pygeos, Cython, Pyrobuf and Cykhash) that needs to be successfully installed before Pyrosm works. Most of these libraries should be very easy to install and Pyrosm handles them automatically when installing with pip. On Linux and Mac, pip installation should work out of the box.