If you want to install Steam, first open the Synaptic Package Manager, wait until it is ready, then in the Search Box (under “Quick Filter”), enter “steam”. You will then see “steam-launcher”. Right Click on it then click on “mark”. After that Click on “Apply” and it gets installed.
When that is done, open a terminal and input:
This will setup and configure steam for your user account. This can take some time.
From now on when you open Steam, just use the Steam menu item within the Menu, under “Games”.