Open WhatsApp on iPhone and log into your account.
Navigate to "Settings" > "Chats" > "Chat Backup".
Select the "Back Up Now" button to start backing up current WhatsApp Data.
Download and install WhatsApp on your Android phone.
Sign in to your WhatsApp account. WhatsApp will pop up asking you whether to restore data from backup for the first time.
Choose on "Restore" if prompted to restore from WhatsApp iCloud and wait until it's done.