Tools often include features to adjust wear levels (float), add any sticker combination, or even apply StatTrak counters.
If you want to experience expensive skins without risking your account, there are legitimate ways to do so:
Many "free" skin changer links are actually delivery systems for keyloggers or "account stealers" designed to hijack your Steam credentials.
Because skin changers modify game memory—the same method used by aimbots or wallhacks—VAC often treats them identically. A ban is permanent and will lock your entire Steam inventory.
These changes are typically only visible to you. Other players on the server will still see your default weapons.
Most "inject" themselves into the game's memory or replace .dll files to override the textures provided by Valve's servers. The Truth About iChanger and "Free" Tools