Many full time photographers are generally familiar with these guidelines, but it’s always good to get a refresher on them, as well as educating non-photogs about everybody’s rights as American citizens when it comes to taking photographs in and of public buildings and spaces.* So if you’re just curious about how it’s supposed to work (keyword “supposed”; it won’t stop people—both other civilians and law enforcement officials alike—from taking offense and challenging you if they feel agitated by it; it’s up to you do decide how far you’re willing to go to stand up for yourself or avoid trouble). It also discusses your limitations when you’re on someone’s private property (they set the rules, and you must abide by them).
*Disclaimer: I realize there are many people who view the ACLU (the source of this web article) with disdain and hostility due to its alleged political leanings. Just try to ignore the messenger and focus on the content, as it is not pushing a political agenda beyond the affirmation of all of our constitutional rights. Thank you.