A sleeping bag is a critical part of playing Rust. When placed, this item offers a respawn point directly on top of it. It can be named, given to a friend, or even be picked up by it's owner by using the interact key on it.
After death, a menu will appear displaying your sleeping bags and beds by name and you can select whichever one you need. After being used, or being placed, there is a 5-minute cooldown period before being able to spawn on it.
When possible, you should upgrade your base's respawn point to a bed, which has a drastically shorter cooldown timer.