IVs are shortened for individual values. They determine how strong your Pokemon is. Your Pokemon can have 31 IV in each stat: HP, Attack, Special Attack, Defense, Special Defense and Speed. The more IV in stats your Pokemon has, the stronger and competitively better it becomes. You can't increase IVs with training, you can only get better IVs by breeding. To get better IVs you need to have two Pokemon with high IVs, at least 90%. Then, use /ivs *slot* to check what Pokemon has higher IVs and put a Destiny Knot on it. Destiny Knot is the key to getting Pokemon with high IVs. The Destiny Knot passes down 5 out of 6 IVs from a Pokemon holding it, meaning if your Pokemon has, for example, this IV spread: 31 HP, 29 Attack, 18 Special Attack, 24 Defense, 9 Special Defense and 30 Speed, it will pass down, for example, the HP, Attack, Speed, Defense and Special Defense. The IVs always pass down randomly, meaning there is no pattern in which the IVs will be passed down. Now that you bred those 2 Pokemon with IVs around 90%, you should get an egg that has IVs at least at 70%. Now, you're probably asking yourself, how to get a good IVd Pokemon when the wild ones have pretty bad IVs. Well, you can buy them off from players, or you can buy a Build-a-Poke, which lets you have any Pokemon you want, and edit it however you want.
EVs are shortened for effort values. Unlike IVs, they can be changed however you like. To check the EVs of your Pokemon, use the command /evs *slot*. Every Pokemon starts off with 0 EVs in every stat. Pokemon can gain six different types of EVs, one of each of the six stats (HP, Attack, Defense, Special Attack, Special Defense, Speed), and each individual Pokemon can gain a maximum of 510 EVs, with an additional limit of 255 EVs per stat. You can use EV training held items to speed up the process. Those items are Power weight - used for training HP EVs, Power bracer - used for training Attack EVs, Power lens - used for training Special attack EVs, Power belt - used for training Defense EVs, Power band, used for training Special defense EVs, Power anklet - used for training Speed EVs, and Macho brace - used for training any EV. Each item on this list increases the EVs in the stat mentioned by 4 EVs, except for the Macho brace, which doubles any EV a Pokemon gets. To increase your EVs fast, do /warp evtrain.