What is it?
Wireframe is a layout or low fidelity structural representation of your product which gives a rough idea how it will look.
How can I use it?
After your research, put aside useful information. Create a Persona and determine the user flow. Sketch roughly screens and components that creates the flow.
When can I use it?
You can need it especially initial phase of the design process before visual design for better understand the core functionality of the product. Also for collecting productive feedback from user, you need to show something concrete. At this point, wireframe can be your helper.