Where the number comes from is up to you: a lead form, a business card, a missed call.
Ten seconds later it has a WhatsApp conversation, from the same inbox your team already works in.
WhatsApp has one rule for businesses that write first: the opening message has to be an approved template.
The Composer handles it. On a new WhatsApp chat the reply box switches from Reply to Template, you pick one from your approved list, and it goes out.
Once the customer answers, the conversation continues like any other.