Open the app, insert the phone number and tap on the WhatsApp or WhatsApp Business (only if installed) button to start a chat with the provided number.
Alternatively select the number and use "Open with -> MooConnect" to open the app with the number already inserted!

MooConnect is completely free and without any advertisement, created from who, just like you, was anoyed from having the address book always full of useless contacts 😜