The long term stable release at the time of creating this tutorial was QGIS 2.10. At present, it is 3.10.
Please let us know the issues you are facing in a particular tutorial due to version difference, We will give you the solution and let you know what exactly to do.
Alternately, you can also download and install the older version QGIS 2.10 and practise the tutorials.
The procedure to download and install QGIS 2.10 is demonstrated in the "Installation of QGIS" tutorial for Windows 10, Linux, and also Mac Operating Systems.