Individual Values (aka IVs) are essentially a Pokémon's genes. Every Pokémon has IVs for each of their stats (HP, Attack, Defense, Special Attack, Special Defense, and Speed). IVs range between 0 to 31, with 31 being the best. The higher the IV is, the better their stat points are. For example, if a Pokémon has 31 IVs in Attack, their Attack will have 31 stat points more than one with 0 IVs. Basically, a Pokémon with an IV spread of 31/31/31/31/31/31 is essentially flawless (excluding the effect natures will have on it). Most Pokémon have their IV spreads determined by a pseudo-random number generator in the game, which also "randomly" generates stuff like what natures they'll have or whether an inaccurate move misses in a battle.
There really isn't a guide I know of for building a in-game team, but there are a couple of articles that might help you. Smogon's HGSS In-Game Tier List is pretty accurate list of all of the best Pokémon for HGSS in-game play. I also suggest gearing your Pokémon team towards dealing with each of the Gym Leaders and Elite Four so that you don't have any issues with them. We have a Guides & Resources sticky for stuff like this.
Anyway, having others build a team for you is discouraged here, but even so, you may ask for team building questions in the In-Game Team Questions. But before you post, it's best to have some sort of idea for what you're going for (which starter Pokémon do you want, any particular Pokémon you would like to have, etc.). With that said, only threads with teams that are mostly complete are allowed, so I'm closing this.