Theodore,
If you have an Apple Music subscription, you may stream any track, or download a copy for offline listening at no additional charge beyond the monthly subscription fee. The downloaded tracks will be playable as long as your subscription is active. See details in here: Add and download music from Apple Music - Apple Support
You still have the option to purchase tracks for your "permanent" collection, from the iTunes Store or other music download retailer. These are typically around $1.29 (US) per track. (Most folks who have an Apple Music subscription will purchase few if any tracks.)