A multivitamin brings a spread of vitamins, and sometimes minerals, together in one serving. Each nutrient has its own role in the body, and a multivitamin is a convenient way to help fill everyday gaps when your diet is not as varied as you would like. It works alongside food rather than replacing it.
Labels list each vitamin with its amount and, usually, the percentage of the nutrient reference value (NRV) it provides. It is worth looking at the forms used, such as vitamin D3, methylcobalamin or folic acid, and checking whether vitamin A is supplied as retinol or as beta-carotene, because that affects who the product suits.
Some multivitamins are liposomal, which means the vitamins are enclosed in tiny phospholipid spheres called liposomes. Whatever the format, the key habit is to add up what you get from all your supplements and fortified foods, so that no single nutrient goes above the levels considered safe. Taking several products at once is the most common way people end up with more than they need.