I would suggest going to ‘Browse Help’ in Paratext, and checking out the topic “How do I add a term or phrase to a Project Biblical Terms list?”
One thing it suggests is going to a source text (I’m using the HEB/GRK text) and right clicking on a word (in Black), or a lemma (in Blue). One of the options in the right click menu is ‘Add to project Biblical Terms for ___’. I believe you can further modify these, for example to divide them into different senses, but someone else will have to comment on that.