Linear Regression Slope is designed to show how much one should expect prices to change per unit of time.

As the Slope of a trend first becomes significantly positive, open a long position. Either sell or open a short position as the Slope becomes significantly negative.

For information on more ways to use the linear regression outputs of Slope and combining them with r-squared values it may be helpful to refer to The New Technical Trader by Tushar Chande and Stanley Kroll..