Use it anywhere you'd use butter, lard, or cooking oil. Fry eggs in it. Roast vegetables in it. Sear steaks in it. Make French fries in it. Season cast iron with it.
High smoke point (~400°F) makes it ideal for high-heat cooking. Adds a subtle beefy richness to whatever you cook in it.
Tallow is rendered beef fat from pasture-raised cattle, slowly melted down and filtered until pure. A stable, traditional cooking fat that humans have used for thousands of years.
Store in a sealed container in the refrigerator for up to 6 months, or in the freezer for up to a year. Room temperature is fine for shorter periods (a few weeks) in a sealed, clean container away from light.