OK. The 525 is one nice box, no? Have you tried running program material through it and LISTENING while you twist the knobs and punch the switches? Maybe we have a bit of a language barrier here, as well.
The "Ceiling" control adjusts 2 parameters at one time:
As you turn the the knob clockwise, it lowers the Threshold (to increase compression), and at the same time, it raises the output level ("make-up gain") in relationship to that. The result is that the engineer can make gentle changes to the dynamics without abrupt shifts in the apparent loudness of the program. Does that help?
Since you state that you're wanting to use this unit on vocals, you better learn to use the "D-S" (De-essing) function as well. This sets the 525 to provide a harder limiting to the frequency spectrum that contain the "S", "TH", "C" sounds that can "smear" the recording of vocals. In English, we call this "sibilance". If you don't comprehend this, try saying this into a mic run into the 525:
"Sexy Susan Sold Seashells by the Seahore". Do it first with the D-S off, then again with it ON. Hear the difference? OK...
Now, you also asked in another post about the release times and which to use. In general, the lower the frequency of the source (say, bass guitar), the slower the release time you'll want to set. Try the "0.1" or "0.5" for vocals, "2.0" for bass...OK? Once again LISTEN to the changes you make to the program material. This is how we all learn.
And, finally. There are very good reasons that the folks here set up your profile questions asking for your location. Just because we have George Bush as our President here, that doesn't mean we suspect you as a terrorist! If you will tell us what country you are from (and what your native language is), there may be somebody on this forum who speaks it, and can better explain the operation of some of this gear. Comprende usted, senor? BUENO! Hasta la vista, hombre!