Tcl is a scripting language and stands for "Tool Command Language". Tk is a GUI built on top of Tcl and is an abbreviation for "Toolkit".
For a quick-start introduction in scripting, see Cameron Laird's column in SunWorld, called "Regular Expressions", which kicked off with this article:
Look for more info about Tcl/Tk at:
WiKit, the software for this wiki, is also written in Tcl/Tk, as is Wub, the webserver that hosts the wiki.
#Create three different labels
label .l1 -text "This is what the default label looks like"
label .l2 -text "This is a yellow label on a blue background" \
-foreground Yellow \
-background Blue
label .l3 -text "This is a label in Times 24 font" \
-font {-timenew family -size 24}
# Put them in the window in row order
grid .l1 -row 0
grid .l2 -row 1
grid .l3 -row 2