These Miniconda installers contain the Conda package manager. Once Miniconda is installed, you can use the conda command to install any other packages and create environments, etc. For example:

$ conda install numpy
...
$ conda create -n py3k anaconda python=3
...

There are two variants of the installer: Miniconda is Python 2 based and Miniconda3 is Python 3 based. Note that the choice of which Miniconda is installed only affects the root environment. Regardless of which version of Miniconda you install, you can still install both Python 2.x and Python 3.x environments.