There are two parameters of interest in linear regression, r and β.
r tells us how well y can be predicted by x and β tells us what unit change on y we expect to observe given a 1 unit change on x.
To explore how r and β are related, use the sliders on the left to set the σ for x and y and the r between them. A data-set which matches the given values will be plotted with a fitted line, which depicts β.