Enchant a pickaxe, axe, shovel, or hoe at an enchanting table and look for Silk Touch
Use an enchanted book with Silk Touch on an anvil
Trade with a librarian villager for a Silk Touch enchanted book
Find Silk Touch enchanted books in loot chests
Fish up a Silk Touch enchanted book
Use the `/enchant` command if cheats are enabled
Combine a Silk Touch book with the desired tool on an anvil