Skins in the game Rust are cosmetic items that change the appearance of weapons, clothes, tools, or building material without affecting their characteristics. They allow players to personalize their items, giving them a unique look.You can obtain skins either by buying them for real money from the in-game Steam store or trading on specific websites, which is allowed to do. Some items are obtainable free via events or Twitch Drops. To put the skin on your item, open your inventory, right-click on that item, and choose an option named "Apply skin.".

Skins can also be created by players using graphic editors, but for them to appear in the game, they have to be uploaded via the Steam Workshop and approved.

Twitch Drops

You can get free skins by watching streams of popular players in Rust who have Twitch Drops enabled. You will need to link your Steam account with Twitch to do this. The thing is that these promotions are usually held in relation to some events, so keep your eyes on community announcements.

Random objects in the game

Rust features random drops for items, which may include skins. This is easy since one has to just play and be active in the game, but the skins received will be random and not necessarily valuable.  

Promo codes

Quite a number of websites and platforms run giveaways from time to time, like DMarket, Skinlords, Twitter, and Rust Discord communities. What the community is often asked for is just to sign up or even take part in some activities.  

Steam Market

Of course, skins can be acquired for free using credits or via trading; this will certainly take time and patience as you try to accrue the funds from the market fluctuations.

Custom Designs

You can make your skins via Steam Workshop and then use them in-game if the community accepts them, provided you're creative enough. Such options allow players to get the skins they want without having to pay for them, but one should follow the updates in the community not to miss emerging opportunities

Summary

Skins within Rust are cosmetic items that would change the look of weapons, clothes, tools, and building material without touching their functionality. One would be able to buy such skins from the Steam Store, trade with other players, or get them for free in events, Twitch Drops, or random in-game drops. Promo codes, too, coming from various sources, create possibilities for one to win skins. Skins also can be created and uploaded via the Steam Workshop, but they have to be community-approved to be used in-game. Keep up with events and promotions to get your desired skins without spending money.