Well, to make a comic strip on PowerPoint, you need to plan your story. Decide on the panels and what will happen in each. After that, insert relevant pictures or draw your own elements. Don't forget to play with colors and fonts to make it look appealing.
It's not too hard. First, open PowerPoint and choose a template that suits your comic style. Then, start adding your images, text boxes for dialogues, and use shapes and lines to create borders and effects.