Let us create a new environment called fenics and install under this.
conda create -n fenics -c conda-forge fenics mshr
You may also want to install some other packages
conda install -n fenics -c conda-forge ipython notebook matplotlib scipy
Now activate the environment and do your Fenics work
source activate fenics
After you are done working with Fenics
source deactivate
Show list of installed packages in this environment
conda list -n fenics
Update the packages in this environment
conda update -n fenics -c conda-forge --all
First install Docker; this is easy on a Mac and needs some configuration on Linux, see here. After this, start Docker and install the fenics script
curl -s https://get.fenicsproject.org | bash
Then install a Fenics image
fenicsproject pull
You are ready to work with Fenics. Go into some directory where you want to do your work and do
fenicsproject run
Many things like plot windows will not work in Docker, so I prefer using the Conda option to install Fenics