Quick Youtube Video Tutorial
Step 1
Here is where you do your daily missions, after reaching 100 activity from the various ways you can earn it...
Step 2
When finished with your dailies you can go to this page to choose the character of the day to get shards for which rotataes. (when you have them all dupes, you get gems and such instead)
Step 3
As you can see you can also claim fragments from this page, but this is where you'd purchase character with the fragments you own or the universal fragments. (will explain in extra section)
Extra (Mirage Pass And Universal Shards And Costume Shards)
At this time of writing the pass hasn't gone back up yet, but when the Mirage Pass runs it gives another way to earn soul stones, sapphires, rubies, and of course universal character AND costume fragments. (same thing goes for unlocking costumes you can do it this way as well, and will make a further section if anyone is confused)
You basically do the daily missions and the activity goes towards this pass, with numerous points offering universal character fragments and costume fragments which can go (and be combined with character fragments you have for that character) to unlock them.
Where/how To Exchange For Skin Unlocks
When you do gather the costume shards from the Mirage Pass, events, or otherwise you go to the character you'd want the skin for and in the bottom right you are able to use the skin fragments too unlock it from there to.
Source: https://steamcommunity.com/sharedfiles/filedetails/?id=2801415502