Linear regression is a statistical process of constructing a model to explain the degree to which one variable's change (x) can be used to explain another variable's change (y). If the model fits the data well it can be used to predict values of y that can be expected based on values of x. In it's most basic form, linear regression is the straight line that minimizes the distance between all of the two dimensional (x,y) coordinates in a data set.
This video demonstrates simple graphical techniques for building a linear regression model in Excel and explains key outputs that excel generates.
Linear regression is one of the most commonly used tools in data analysis and Excel has many tools devoted to it. The tools include speadsheet functions, graphical tools, Excel Add-ins and third party Add-ins - far too much to cover in a single video. This tutorial covers graphical approaches to linear regression as well as the LINEST function.
For more comprehensive discussion of the statistics involved with building and interpreting regression models using the Excel Add-in found in the Data Analysis Toolpak see this tutorial.