Schema is a structured information in a very specific way that is presented in the HTML code only readable by bots, to understand certain aspects of your site
For example if your site is about cooking and you do a recipe, you can put in that
schema code certain aspects like the cooking time, the ingredients, instructions, etc...
The interesting thing is that if you have a rightly well coded site, you could input that info in a back end (for example a text box to put all the ingredients in the wordpress backend) and then use the information to present it to your user in the site and at the same time, present it to the bots so they can read it in a structured way
There are plugins that do basic schema operations, like structuring basic articles, news articles, and some basic info about your site (like the name of the site, and other general schema aspects). Most SEO plugins do this by default like Rank Math.
But there are also certain plugins that perform a very specific function, like organizing certain type of content (like cooking recipes), that will offer you both the possibility to create recipes and present that schema at the same time.