If you want to do something every x seconds, you are going to need a way to measure time pretty much like a counter. You can take a look at a previous answer I gave here :
For the display part, if you want your code to be modular, for example be able to add, swap and remove steps from your story and have text/images to appear, you are going to need to store them inside a list or some iterable data structure.
A pseudo code would be (using JS objects) :
const steps = [
{text: "In a galaxy far, far away..."},
{image: "image_1.png"},
{blank: true},
{text: "Yoda is cool", image: "yoda.png"},
// ...
];
and I found a few examples by googling “p5.js story” so maybe that helps (although I cannot find the one I saw before - which was full screen and an elaborate narrative with p5.js)
but - if your question is more about making a “website” than just making a sketch, then I would recommend you to use DOM instead of canvas (and I would even go with standard JS without p5.js). The upside is that it gives you more freedom with typography and layout that can be adaptive to different window sizes and mobile. The downside is that it is more confusing than canvas because you need to work with CSS for layout and style and not just placing images and texts within a canvas.