On this page of the Cyberpunk 2077 game guide, you will find out what are the so-called Skill Shards. These items are used for character development.
Skill Shards can be found along with loot – in containers or found by the bodies of defeated opponents.
Each skill splinter adds "free" XP to the corresponding skills. You do not have to manually "activate" it. Just pick up the splinter and you will receive a prompt saying that you have been assigned experience points.
Thanks to Shards, you can promote your skills faster to the next levels. After opening the character menu, you can view various skills. In the lower left corner of the screen, you will always see a progress bar for the given skill.
In addition to finding the Shards, you can also develop a skill by performing related activities, such as sneaking around, using specific weapons or performing actions requiring strength. Upgrading skills to the next levels is always rewarded – by e.g. free perks points or various permanent bonuses to V stats.
There are also much rarer Perk Shards. Each of these shards gives you 1 free perks point. This can be a good way to improve your character by unlocking the most useful perks faster.