ragdoll resizing help

hey all, new to the forum, and a bit new to computers. anyway, I’m trying to re-size rag dolls.
i have the tutorial page here: http://vggtsworld.ta-host.com/where/garrymod/mscaledoc.html

now I read through the steps, but one step asks: Open your Steam client. Select the 5th tab and select the Source SDK.

what is a Steam client? and how can I get to it? like I said, I’m fairly new to computers, so ANY help at all would be awesome

Wait wait wait… you’re trying to resize ragdolls for garry’s mod, and you don’t know what the steam client is? That thing that you use to access garry’s mod in the first place? Either you are overstretching yourself here, or… fuck it, I’ll let DJ Tiesto explain.

If you don’t like techno remixes, it’s He’s a Pirate by Hans Zimmer and DJ Tiesto.