Many tutorials here don't describe basics things. We understand that for many merchant's (especially for new prestashop users) it's hard to understand even "basics". So I decided to explain also this one.

How to get category ID number?

It's very easy. Just go to the Catalog > categories tab in your back office. And you will see all categories defined in your store. You can also find there each category id, just take a look on the picture below:

How to get category ID in prestashop?