Use collections/collection-handle to display the tab on all the product pages from a collection. Eg. a Sizes Chart tab on Women collection would be collection/women.
Use product/product-handle to display the tab on a specific product page. Eg. a Features tab on the product called Art t-shirt would be product/art-t-shirt.
Use global or global/anything (if you want to avoid having similar item names) to display the tab all product pages. Eg. a Shipping info tab on all products would be global.
If you have a tab that needs some different content for tens or hundreds of different pages, for example a tab called "Features", you might end up with tens of pages called Features and struggle a lot when it comes to selecting the right one in the navigation dropdown (see below).
To avoid this headache, rename your pages using double pipes ||
For example, the page Features becomes Features || Product XYZ or Features || Cool T-Shirt. This way, you can find the right Features page fast. Everything after the double pipes || in the page title won't be displayed in the tab title. For example, the tab will still be called "Features".
If you enabled the product Reviews tab, by default it will be displayed as the last tab at right. To
it, add a #Reviews item in the product-tabs navigation menu and then drag & drop it to the order that you prefer.