Why won't the turn signal blink but light bulb is on?

Thanks for your answer. I'm pretty sure they're installed correctly. When I turn on the emergency flashers, they all blink like they're supposed to. These are the same bulbs that don't blink on the drivers side when the turn signal is on. I'm pretty confused! Any help will be appreciated. Trying to avoid a high doagnostic fee in an electrical shop.

Could you give me a little more detailed answer please? Someone suggested the turn signal switch. Are these the same thing? What is the "flasher"? Thank you!