US law requires all OTC drug labels to follow the same "Drug Facts" format, so once you know how to read one, you can read them all — the sections always appear in the same order.
"Active ingredient(s)" lists what actually treats your symptoms and at what strength. "Purpose" tells you what each active ingredient is for (e.g. "pain reliever," "antihistamine"), which matters most in combination products with several active ingredients.
"Uses" and "Warnings" are the two sections worth reading closely every time — Warnings covers who shouldn’t take the product, drug interactions, and when to stop use and contact a doctor. This is where you’ll catch overlaps with other medications you’re taking.
"Directions" gives the dose and how often — pay attention to age-specific dosing and maximum doses in 24 hours. "Inactive ingredients" lists everything else (fillers, dyes, flavoring), which matters if you have allergies to specific substances.