Assuming you know that there are 4 pkmn gens: Gen 1(Kanto), Gen 2 (Johto), Gen 3 (Hoenn), and the recent Gen 4 (Sinnoh). Each gen has 3 different main games that let you explore the regions, but if you want to start from the beginning of pokemon then I suggest you get either HeartGold or SoulSilver versions. It would probably be hard to obtain the orignal Silver and Gold or the first pokemon games Blue and Red nowadays so these game s are your best bet to experience the 'beginning' of pokemon.They're for the DS so if you have one then get 'em. They're both great games and you can obtain all the pokemon created to date in them (through trading of course).
Other than that I suggest Platinum version (it's for the DS too, just an updated version of Diamond and Pearl) and Emerald if you don't have a DS and would rather pick up a cheap $30-$50 dollar SP (how much I think they cost) to start you off in the pokemon world. Emerald is a great game and will definitely give you an amazing chance to see why Gen 3/Hoenn region are awesome.