Individual control snapshots: Place the now time where you want to take the snapshot. Right-click on the control whose state you want to enter as an automation node, then select Automation Snapshot. This places a node on the automation envelope.
Doing a snapshot of a parameter in all tracks: This is more complicated but Quick Grouping makes it simpler. Remember, though, that Quick Grouping works only on tracks of the same type (audio, MIDI, buses). We'll assume you want a snapshot of the audio track Volume levels. The object is to set all tracks for Automation Overwrite so once your levels are set, when you hit play these levels will overwrite any existing automation to create your snapshot.
Select all tracks. While holding down Ctrl, select Volume for the edit filter. While still holding down Ctrl, click the Automation Write button. Open an Inspector for the selected track and click the Track tab. While holding down Ctrl, select Overwrite under Automation Write Mode. If Read is enabled, hold Ctrl and click Read so all reads are turned off. Now all your tracks are set for Automation Overwrite.
Click Play, and automation nodes will be entered for the levels you set. Keeping playing until you want to do another snapshot. Stop. Turn automation write off, then play the section so you can set the levels as desired. Once that's done, set the now time where you want the snapshot, re-enable automation write, and click play.
This sounds more complicated than it is...once you set up the first snapshot, the rest are pretty easy as you move through the song. Just remember to turn off automation write when you're checking out what levels you want, otherwise all your fader movements will be written. Of course, if you play around with the levels after where you want the snapshot, you can just overwrite them by continuing to hit play after the snapshot.