It depends. Most good supportive shoes have some arch support built-in. If you are wearing flat shoes, or have some pain/fatigue/aching in your arches or legs arch supports can be a good idea. Start with an over-the-counter arch support first, and if you still have issues see a podiatrist.
Orthotics. If you need orthotics, then yes. However to determine that, see your podiatrist and discuss any foot pain or issues you are having and he /she will determine the need for orthotics.