Automation

Read Mode: Plays back all automation on the track. If volume data exists, for example, the volume fader will move during playback, following the prerecorded automation on the track. You can’t change the value of the chosen automation parameter by moving controls when in Read mode.

You can draw dots on the line in this mode.

Touch Mode: Plays back automation in the same way as Read mode. You can modify the value of the chosen automation parameter by moving controls in Touch mode. After the fader or control is released, it stops writing the automation and goes back to just reading it.

Latch Mode: Works like Touch mode, but after the fader or knob is released, the new value replaces existing automation on the track. So wherever you left the fader or knob when you stopped touching it this value will be written for the rest of the track until you touch the control again.

Write Mode: Erases existing automation on the track as the playhead passes over it. Records the new control movement or deletes the existing data if you do nothing. This means is you have multiple automation on a track it will erase it all when writing new information. Logic does warn you about this mode!

Don't forget to change automation to read mode when you have finished automation. If you don't you might be creating automation by accident!

Here is a pretty good video on the basics of automation. Take a look.