I assume you’re referring to using dashes to get in?
There are two basic ways to use dashes, and both of these are, incidentally, extensions of element 01 and 03 in the footsie handbook. You either want to use an offensive dash in reaction to a button your opponent throws out (since that means they can’t hit you out of the dash), or at times when your opponent is unwilling to push a button.
A very good set to study if you want to see offensive dashing in action, is the following set between Kuroda’s Makoto and MOV Chun-li in 3S. The very first round of that set is a textbook example in how to apply dash-ins. When you’re watching this, look for times where it would feel natural for MOV to not press buttons (Kuroda got a lot of dash-ins at times like this), or times where MOV whiffed something and Kuroda dashed as a response.