[Grand73Am]

The first and easiest thing to check is the battery itself. If it's not a sealed battery, pry off the caps and check to be sure it has water up to the inner rings in the cells. It may have dried up and needs water and might still hold a charge if you have a battery charger to put on it. While you're at it, check the terminals for corrosion. Clean all corrosion off the battery cable terminals and the battery posts by scraping with a knife or use a battery terminal cleaning tool, available for cheap at the parts store, and reconnect them and see what happens. It may just be a corroded terminal or it could be the battery has died, due to being dry, or to having a bad connection, so it wasn't getting charged up properly. Sometimes it's that simple.
Another easy check would be to use jumper cables to jump your car off with another car. If your cars turns over with a jump, you know your starter is fine.
If you don't have a battery charger, you could take the battery to a store, like Autozone, that checks batteries for free to see if it's still any good. If it's bad, a new battery doesn't cost much with your trade-in.

If the battery is good and the cleaning doesn't work, then you have to look for other causes like the starter connections, as mentioned above.