There are two organizational concepts in Knapsack that should be considered when defining your library structure, namely the Left Nav and Pattern Page Tabs. Both are designed with flexibility in mind.
The Left Nav the searchable list of top level topics. Pages and Pattern Pages can be organized into Groups, these items are infinitely nestable. Rearrange the Left Nav items by clicking the Edit button at the bottom right of the nav to enable “edit mode”.
When in “edit mode”, the items in the Left Nav will display drag handles to the left of each item. Simply drag items to reorder them. While dragging an item, dragging left or right will adjust how it’s nested with the item above it. Be sure to Save any changes made to the Left Nav when you're finished.
Pattern Page Tabs
Pattern Pages are capable of containing any number of either Content or Template tabs. You can even have multiple tabs of the same templating language to display different templates of the same pattern (e.g. maybe your primary and secondary buttons use separate templates but you want them grouped on the same Pattern Page).
Explore how Pattern Page Tabs work here.