Ableton's Learn Live series walks through the Modulation tab inside the Echo device, covering the two modulation sources available: an LFO and an envelope-follower.
The LFO can target both delay time and filter frequency. Amount percentage controls how much the delay time and filter shift, rate can run free or lock to your project tempo, and several waveform shapes let you dial in whether the modulation feels smooth, stepped, or somewhere in between.
The envelope-follower adds a second layer that responds to the amplitude of the incoming signal rather than a fixed clock. A blend control lets you mix both sources, so the delay can react partly to a rhythmic LFO and partly to the dynamics of what you're playing. Pushing the envelope-follower to 100% removes the LFO entirely, leaving a delay that breathes and shifts with the signal itself.