This is the time of question where I don't know even where to start, so i'll describe what I have and what I want, so that someone maybe could give me a direction to go. I'm not asking for code, just for what approach to take.
What I have
I have a Wordpress website, with some static content and stuff, all content was added via the public available plugins and the easy to use customizer.
Also I have a custom built website in php which an android app uses to work, it has it's own database (under the same host that runs wordpress) and store all the info about products and users. there is no visuals the website works just as an api.
What I Want
I wonder how would I integrate the two, make a page where the wordpress website is able to list products from my custom api. How can I ( Or how should I ) run custom php inside of wordpress so that for example I could show a list of products fetched from the other database via my custom api.
I started to build a wordpress plugin where I would create a widget that does all this, but maybe someone who understands better how wordpress work should have a better way of doing things.