Miracast is a standard for wireless connections from sending devices to display receivers. It allows you to cast your screen to a TV or projector without messy cables. If you are using Windows 7, you might find that setting this up is a bit different than on modern systems. Understanding Miracast on Windows 7
Before you look for software, your computer's hardware must be physically capable of supporting wireless display technology.
What are you trying to cast to (Samsung TV, Roku, etc.)? Are you open to using a physical dongle like a Chromecast? I can give you the exact steps for your specific setup.
Visit the website of your GPU manufacturer (NVIDIA, AMD, or Intel) and download the latest "legacy" drivers available for Windows 7.