One easy way consists in enriching the currently viewed glossary with text that you have copied to the clipboard:
Even more powerful, you can enrich the currently viewed glossary based on documents that you have typed in the past, via the Tools → Enrich Glossary from Documents menu. It allows you to obtain glossaries that reflect the subjects on which you are writing, with their frequent words and phrases.
To compile a glossary click on the Add button to add the documents you want to compile, update your Compilation Settings if needed, and click on the Compile button.
At the end of the compilation the results of the compilation are displayed in a window, and you can choose which entries you want to enrich your glossary with.