We recommend users to use the Anaconda distribution. You can then either install Brian 2 in the Anaconda root environment, or create a new environment for Brian 2 which has the advantage that you can update (or not update) the dependencies of Brian 2 independently from the rest of your system. The packages for Brian 2 are in the conda-forge channel, to install it use:
conda install -c conda-forge brian2
If you do not want to use the Anaconda distribution you can also install Brian 2
from the Python Package Index with
pip install brian2
It is highly recommend to make sure that Brian is able to use C++ code generation, have a look at the documentation for more details.
You will most likely also want to install additional tools to work with Brian 2, in particular Python's plotting library matplotlib and the development tools from the jupyter project. To install them, use the same tool as for the installation of Brian, e.g.:
conda install matplotlib jupyter
pip install matplotlib jupyter
Also have a look at other Brian-related packages.