How to do the Cron job in wordpress?

Hello,

I am working on a car dealership website and we are using a plugin to publish car listings.

Now I want to make a functionality or a plugin which will pick the csv file from the server and read the file and then import csv file data into website.

It should also update the plugins listing data and also update and add new records in database.

I want this process to run twice a day

I tried to check the cron tutorial of wordpress but when i used the add_action hook in my custom plugin it gives me a fatal error that

call to undefined function ‘add_action’;

I am really confused how to do this?

I just need to add a functionality by which It can import and update csv file data into website and can update listings information of other plugin that is being used to show listings on website

Thanks,

Junaid