League of Legends (LoL) Question: How to make item sets

Alright, it is not entirely clear to me what exactly you want to know, so here the questions you could possibly mean (& including the answers of course).

What are item sets?
The ingame shop has 3 tabs: Recommended, All Items, Item Sets. Obviously we're talking about the 3rd tab here. You can modify item sets by going into collection backpack icon -> items.

There you can see your current item sets, import item sets & export item sets (3 buttons at the top).

How do I import item sets?


How do I export item sets?

First you have to make an item set obviously. Then you click this button:

Then you select whether you want to copy it to clipboard or export it to a file.