"Guide Priority" is the hierarchy of guides you can automatically assign trips to. You can base this on experience, education, skills, etc. You can drag and drop to reorder them any way you want.
To set Guide Priority:
1. Click Company, then click Users
2. Check "Use Guide Priority"
3. Then choose the Category for which you want to prioritize your guides
4. Drag and drop guides
5. Exit out of the window and it'll save automatically