I'm lost , well I think I am so can someone tell me what do I do after..

I've never heard of Aspiration Lake... I'm guessing it's that new one, forgot what it was called >< It's located in the middle of Route 214, to the right. You'll be in [forgot what it was called] and if you go down the wall using Rock Climb, you'll be in [some cave that I forgot] where time is distorted and rooms are random. If you keep randomly going into rooms, you'll eventually enter the room Giratina is in. However, if you enter the room in which you just came from, you'll start from the entrance.
You'll need Defog and Rock Smash so the place can be much easier for you.

There's also the Eastern Island, which you have access to from Snowpoint City. That's where the Battle Tower is. There's also Stark Mountain that you should look into. You can fight/catch Heatran there.

Well one thing that you could do is get Garitina. What you do to get him is go down to the Spring Path ( Which appears after you get the national Poke'dex) You go into the very confusing cave but keep going straight and you'll be okay. You need rock smash. A lot of Rock Smash! When you finnally get to Garitina hews on lvl 70. Youm could do alot of other things such as go to Stark Mountain and catch Heatran (lvl 70) Go to full moon Island and unlock Crysallia (also lvl 70) or you can catch Rotom in the Deserted Poke'mon Mansion ( lvl 15 ). Eityher way you go it's still very complicated and you need very strong
Pokemon to do all this. Hope this helped please rate :P

You can catch Heatran at Stark Mountain, access the battle tower, catch Giratina at the Turnback Cave, and much more!

You can go to snowpoint city or canalave city and take the ferrys to different islands. Um..migrate Pokemon, get you're Pokemon to lvl 100. Tons.

Ok the full list of Pokemon you are able to get.

Cresselia-After you have beaten the elite four and gotten the national pokedex, find the house in Canalave City that is above the ship. The little boy is having nightmares. Darkrai is giving him a hard time apparently. Talk to the mom, and she will tell you about him. Go outside and talk to the man with the ship. He will take you to Cresselia's island. Go into the forest and find Cresselia. It will run from you, and after that use the marking map app to find it roaming around from place to place.

Giratina-Once you have the national pokedex, go to route 214. A new opening will be there. Follow it, and use rock climb down to the enterance of the Turnback Cave. You must reach three pillars. Once you have, any room will take you to Giratina. Catch it, if you want.

Heatran-When your rival wants you to go to battle tower with him, get the national pokedex. You can access Stark mountain, where Heatran lays. Hope this helps!

Glad to be of service, Hyrules_Hero