A show usually has a leader reference tone and also has pops, known as sync pops or head pops (versus tail pops) or casually just called "2 pop". The reference tone is in regard to calibration level, the 2 pop is (secondarily for calibration) but primarily for ensuring sync - especially when we';re talking about ProTools sessions containing the complimentary sound assets pertaining to the show. The tail pop is basically the same, but to ensure there is no sync drift, as would happen if an incorrect framerate was utilized or Drop vs No Drop when in 29.97. These get printed to stems and printmasters for the same reason, to ensure sync for layback.
The reference tone of 20dBFS is in reference to the fact that this tone should be pegging the meters at -20dBFS through the entire signal chain, and the mains should calibrated as such that -20dBFS either projects at an equivalent sound level of 85 dBSPL (theatrical dub stage), 82 dBSPL (near/mid-field stage or edit suite), or 78/79 dBSPL (TV sub stage). Really depends upon what work you do. But this reference tone assumes that you have already utilized pink noise with an RTA to calibrate your system to the appropriate SPL reference level across the entire frequency spectrum on the mains. So while pink noise (the Dolby file is the best one out there) is for actually calibrating your mains, the reference tone is for the internal signal flow leading up to the mains. Which, if you pinked correctly, the tone should hit you at an appropriately, but comfortably, present (but not loud) level.
20dBFS also tends to be where the dialogue RMS sits in the mix in a theatrical mix. Peaks of normal dialogue tend to hit around -12dBFS, with loud projections around -6dBFS. But the average energy of your dialogue will sit right in the -20dBFS pocket most of the time. Which, as the reference tone tells you, is an appropriately-present level.
The role of a dialogue EDITOR is to make sense of the OMF and minimally balance the levels "in the ballpark" so that the energy sits in the aforementioned pocket. So in a sense, yes the reference tone is your guide for dialogue levels - but perceptually, NOT literally by the meters. How the reference tone feels perceptually to you, is how the dialogue's presence should also feel perceptually. Mostly, your job here is to edit the material only.
The dialogue MIXER will be taking this balancing out the levels as they should be for a transparent and flowing track.
Let the mixer make the final volume decisions, and don't tie their hands with Normalization, etc. it'll be a waste of your time to do so and you'll be dealing with a less-than-pleasant mixer by locking them into decisions only they are qualified to make.
Hope it helps!