+main stat enchants give the stat (+3 stam, +9 stam, +5 strengh etc) this includes leg and shoulder enchants.
+ secondary stat do not give stats (+5 haste, +5 vers etc)
Some weapon enchants work ( what i have seen so far: elemental force, Dancing steel)
Gear that has things such as "of the eagle" give those stats + the stats you get from filling a slot.
For some classes using a full "of the" set is actually better than getting the 5% from wearing only your armour type, for example on my paladin i actually get 16 more strengh using a full mail set with "of strengh"