In Tasker I first created a new Project and named it "Kustom". You don't need to do this, because it's simply for a better organization inside Tasker of you have to many Profiles and Tasks (no pictures here, just long press on the project bar and then click "add").

To start you have to create a Task that tells Tasker what to do when Whatsapp receives new messages. To do so go to TASKS, press the "+" and name your task. I called it “newWapp”, but the name is completely up to you. Then press the check mark.

This Task has two things to do. First there has to be a Variable that counts notifications and this Variable has to be transmitted to Kustom.

Your are now in the Task Edit screen and the next step is to add the first Action to the Task. Therefore, press “+” at the bottom and choose “Variables”.