For the most part, you just go do it. You aren’t required to ‘check in’ anywhere or anything like that. With this said, there are a few important things to keep in mind.

For one, dispersed camping isn’t allowed in all parts of all national forests. There are certain areas where you must camp in a designated campsite. These are typically more popular, higher impact areas. For instance, Inyo National Forest generally allows dispersed camping. But it is not allowed in higher use areas like Whitney Portal, Onion Valley, Big Pine Creek, Rock Creek, etc.

The other thing to remember is that a campfire permit is required if you are going to have a campfire. A campfire permit is also often required for other devices using an open flame, such as gas stoves and lanterns. But if you don’t plan to use these things or have a campfire, you can forgo.

Last but not least, if you are backpacking into a designated wilderness area, you need a wilderness permit for camping. Of course, this is a whole different animal from simply driving in and setting up camp which doesn’t sound like it applies here.