Is the currently possible to build a lightning component and then use it within a dashboard? If so how do I do it.
The short answer to this is No. There is no way as of today that you can add a lightning component in a Dashboard. There is this idea Ability to add Lightning Components to Dashboards open to allow this feature.
What you can do is instead create a custom tab and use that as a dashboard where you will be able to put your custom lightning components.
You can expose a Lightning Component in a Classic Dashboard, but it will not work in Lightning. As Jayant says, you would want to vote on that idea. To get this working in Classic, you simply need to create your component, create a dependency app, create a Visualforce page, and finally add the page to your dashboard as a new component. See Using Lightning Components in Visualforce Pages. This is only a temporary workaround and should not be relied upon heavily.