First steps

Type /clcinfo to bring up the options window. Click on the + sign near Templates then on Template1, in the left column. You will see some options in the main panel, organised in tabs. Let's configure the main settings for your first template.
Templates are used to group the various interface elements by talent builds. You will need to assign the main tree and one specific talent in order to differentiate between them. The specific talent does not have to be from the same tree, just to be in your build. It is used to differentiate between specs.
Let's say you are an enhancement shaman, a typical way to configure it's to go for the top talent in the main tree, like this:


Now, if you want to make your template work only in your pvp spec, you would use a distinctive talent that you would most likely take only in a pvp spec, like:


Once you setup the template for your current spec the Active Template category becomes populated. Here you will have access to the available interface elements.
Probably you will mostly use icons to display various information, so let's add one to the template.
Click on Icons in the left menu and then on the Add Icon button in the main panel. You can move the icon around by clicking Unlock and moving it with the mouse (don't forget to Lock it back when done) or by adjusting the values in Layout tab.
By default the icon does nothing. You need to specify what you want it to display, so let's check the Behavior tab. Edit the code box and add: return IconSpell("Shamanistic Rage"). When you click Accept the icon will display your Shamanistic Rage ability showing if it's usable or on cooldown.



You can find the available functions in the reference or in the class module pages. If you are not experienced with lua you should check the code samples, look for something similar with what you want to do and just change the name or the id of the spell.

This should get you started for more information check the other sections.