yeah- that chart pretty much says it all:
pt buy is when you start all your stats at 8
str 8
dex 8
con 8
...
and then you use the 28 points to "buy" stat boosts
buying 1,2,3,4,5,6 costs one point each
so going form 8 to 14 costs 6 points
15,16 costs 2 points each- from 8 to 16 costs 10 points
17, 18 costs 3points each- from 8 to 18 costs 16 points
do this for each of your six stats.
with 28 points (total)- you cant really go any higher without really killing your other stats
the best I can come up with is: stat (pt buy)
14 (6),14 (6),14 (6),12 (4),12(4),10(2)
- no negative stats (penalties) and you have a rounded char
16(10) 14(6) 12(4) 12(4) 10 (2) 10 (2)
- one really good stat- one good- couple mediocre ones
16 (10) 14 (6) 14 (6) 12 (4) 10 (2) 8 (0)
- one really good one, two good, and Ok, and one dump stat
If you want- you can start one stat at an odd number (and up at lvl 4) or if your DM starts you at a higher lvl.
the firstone is good for paladin, monk and rangers
the second one is for casters (sorc, bard, wiz, cleric)
third one is for fighetr types and that can afford a dump stat.