To create a link with your phone number, use this link: https://wa.me/number and replace the word "number" with your full phone number in international format. Do not include parentheses or dashes.
You can also create a link with a predetermined message which will automatically appear as an option for the customer. That way your clients can save time when messaging you.
Replace "number" with your full WhatsApp phone number, and replace "message" with your predermined message.
Use %20 between words to include a space.
If you'd like to do the same on your website, use WhatsApp Buttons.