I have inherited a template. Someone showed me that if I create a word document from the template and then type "tcp-t" plus F3, the word document will be populated with additional pages and with text, tables, etc. How do the characters "tcp-t" get assigned that way?

F3 is the activator for what are called autotext entries. You create the desired "text", and then, with this selected, in the autotext dialogue box, copy it into the autotext entry section and then provide a handy "name" for it and save it. In the document, you are then able to type the "name" followed by pressing the F3 key, to populate the document with previously created text, etc.