Pathagoras offers a number of ways of capturing text and adding it to your books. These two are your most likely options:
•Highlight & Add requires only that you (1) highlight the text you want to add and (2) press <Alt-G> next to the highlighted text. The Term Works! screen will appear where you can name the clause, provide its subject and select the glossary into which the term should be added. You do not need to open the glossary—Pathagoras handles that for you (as well as placing the term in alphabetical order according to its name).
•‘Direct add’ involves opening the glossary and either pasting text from another source or typing original text. Then highlight the text and press <Alt-G> (i.e., highlight & add). As you can see, the method at the first bullet probably makes more sense unless you happen already to be in the glossary for other purposes – see below.