The core text of the WW:WW book has been lifted in a huge part, but not wholly (naturally) from the WW:The Apocalypse book. If you have access to that, you'll find a lot of extra information there.
You'll also want to check out The Rite of the Opened Caern on p.169 of the WW:WW book (and in WW:TA as well, if you can.) It explains a lot about how Caerns work.
The chart you mention is featured in WW:TA, but with explanations that somehow got left out of WW:WW.
The footnote for "Power" says: "One point/level/die is gained per success (see Rite of the Open Cairn", whereas the note of "Spirits Encountered" is mostly the same as that of WW:WW.
As for your specific questions: How much, when, and for how long are, I believe, answered by the above quotation, and by the Rite mentioned above. From what range: I believe you can gain these bonuses only in the Caern. As far as I can remember, the powers work only in the Caerns, but I'm not sure about this. Sourcebooks dealing with the Umbra and, obviously, Caerns, etc., may have additional and more precise info, but I don't have them on me atm, unfortunately.
As for why did they release a game with info missing: Probably because of 1) oversight, 2) editorial mistakes, 3) they assumed the target audience is more than familiar with WW:TA already and know the relevant core rules by heart. :)
