Pokemon White/Black Questions?

I beat the Pokemon league and the main story line, and I have found all the seven sages. I have also beat Cheren. I went to the left way at the end of the victory road, where cheren is at and then i moved the big stone and at the doorway at the left there is a little rock in front of it. What do I have to do to get the first legendary trio pokemon, and what am i supposed to do at the abundant shrine. Also, what am i supposed to do now since i have found the seven sages.