How do I enable tabs (a.k.a. drop downs) on my product page?
If the theme you are using does not allow tabs or drop downs for your product descriptions, this is the sort of thing that can be achieved with the use of an app on the Shopify app store.
An example of an app that would work is 'Tabs by Station'. If you install this app to your Shopify store it allows you to create tabs for individual products and also create a tab that will be universally applied to every product on your store.
Here is the link to check out apps that provide tabs for your product pages -
https://apps.shopify.com/search?q=product%20description%20tabs