Pair programming is a software practice where two software developers will share one computer. The one with the keyboard is the one programming and is concerned with the details of implementation. The one without the keyboard is maintaining the bigger picture and the overall direction of the programming.
There will usually be a healthy level of discussion between the pair; the one on the keyboard will often describe what they are doing and thinking, while the other will be calling out the next steps and pointing out any issues.
It's a little bit like a rally car driver working with a navigator. The driver is responsible for focusing on solving the immediate problem, the handling of the car around the course. The navigator has the map, keeps track of their location, and ensures the driver has enough information about the direction being taken and any obstacles...