It's easy to tame one!

Here's a step-by-step guide

Step 1. Find one (in snow biome)

Step 2. Tranq arrow it (watch out they're usually in packs!)

Step 3. When it's knocked out put berries/crops inside it's inventory

Step 4. Don't let direwolves get it

Step 5. Enjoy your new Manny the mammoth from ice age!