If you want to go camping anywhere in the woods, ask yourself a few questions.

Is it in a national park? Visit the web page of the park in question to review requirements and regulations. You can in fact camp in Yosemite backcountry for free - all you do is show up at the right time to get a first come/first served wilderness permit. Same with Sequoia/Kings Canyon. You have to agree to follow their rules and those differ from one park to the next, so review those websites! You will need a bear can or risk a fine. You will leave pets at home. You will not light campfires over 10,000 or 9,000 feet elevation, depending on location.

Is it in a national forest? if it is, check National Forest Service - each national forest has different rules, too. For example - Los Padres National Forest (Monterey district) does not require a wilderness permit but many parking lots near trailheads will charge a small per day fee to leave your car, and you will likely need a free campfire permit to operate a stove or build a fire in any national forest. All of these rules and locations from whence to obtain wilderness permits and also maps are on the website!

Is it in a state park? Look those up too! State park website will tell you where they let you camp, how they expect you to handle it (make reservations? just show up?).

Most everywhere, it is expected that you will make camp at least 100-300 feet from water sources, dig catholes at least 100 feet from a trail or water source, and pack out all your trash (including used tp in places like Yosemite). Some places (a few lakes in the Sierras, for example) allow no camping at all. Your worries are not unfounded - if you are caught breaking rules you may be given a fine.

Some guidebooks will have info on permits but be aware that requirements change - the websites are the place to go to find phone numbers for ranger stations you can call.