Bip39 12 Word Seed Phrase List One example of manually generating entropy will be flipping a coin. But when an attacker provides a coin that's weighted somewhat in favor of heads, your First source of entropy should have been corrupted. To store your Bitcoins you fundamentally need a wallet app. https://thegreatbookmark.com/story18642058/phrases-with-bit-the-basic-principles-of-seed-phrase-generator