EVs... i hope this is enough
Note: I did write this myself, thats why its gonna sound vague and stupid :D
EV= Effort Value
EVs are what you may call the "Building Blocks" of pokemon training. You get between 1 and 3 EVs each time you battle and DEFEAT a pokemon. Depending on the stats of the pokemon, they will distribute EVs accordingly.
If you battle and beat a blissey, it gives you 2 EVs for your HP becuase bliss has a high HP.
For ever 4 evs you gain per stat, that stat is increased by ONE point at level 100. The total amount of EVs you can get per stat is 255. Well techinically 252, cus those extra 3 dun give you any extra stats, which is an extra of 64 points in any designated stats... Pretty high when you think about it.
The macho brace DOUBLES your EV gains per battle. So if you were holding a macho brace when you beat that blissey, you will gain 4 EVs as opposed to two. It will help with your training.
Here are the pokemon in sapphire/ruby that'll give you one EV per stat... which are EASY to find:
HP - Whismur - Cave on Route 106
Attack - Carvanha - Route 119 (Super Rod)
Defense - Sandshrew/Skarmory - Route 113
Special Attack - Spinda - Route 113
Special Defense - Tentacool - Almost Anywhere you can surf
Speed - Zubat/Golbat - Cave of Origin
Good luck... if ya dun understand, head over to serebii.net and read their guide... that thing is huge.
(ALL OF THOSE POKEMON were taken from SPP)