Ableton's Follow Actions let clips trigger each other automatically in Session View, and this bit covers the exact steps to switch them on. In Clip view, clicking the triangle reveals the clip launch settings, where the Follow Actions button lights up yellow when active. A keyboard shortcut, Shift+Return, lets you enable Follow Actions on multiple selected clips at once.
Once active, the Clip Launch button changes its visual style and the next clip set to be triggered begins flashing, giving you a live readout of what's queued up next.