I got a 3x3x9 I for christmas and I have been able to solve the center layer and all below it also the centers ,top edges and top layer. however I cant solve the corner pieces on layers 6,7 and 8 ( from the bottom) does anyone have any algorithms I could use?
Thanks

You need a layer by layer approach for the upper layers. They can be done in groups but it gets difficult to keep track for a beginner. If you get a Roadblock II then this is required.

Do corners first:
Look for headlights - if you have them then turn them to be on the L.
Swap the FR and BR corners using R2 U R2 U' R2 U' D R2 U' R2 U R2 D'
In this scenario the D is the equivalent layer below the equator to the layer you are working on.
Aim to get all 4 corners correct. Place them correctly.

Now swap edges into place:
Opposite edge swap with (R2 U2)x3 note this creates a middle edge "parity"
Adjacent edge swap - R2 U R2 U R2 U2 R2 U2 R2 U R2 U' R2 swaps UF with UR. It also creates the same parity. Ensure that any edge parity that is already present is on the R face so this sequence will undo it.

This will get you most of the way and then you need to correct the edge parities that you have created. Look on YouTube for this SuperAntonioVivaldi shows it on his 3x3x9 tutorial. It's well beyond my bedtime here. If you still need help then let me know.

EDIT: Holy cow. I just realized Puzzlemad's algorithm for the corner swap makes things a million times easier. I'll still leave my modified explanation of the parity fix, but he's just flipped my world upside with that simple change. My wall of text was completely unnecessary and solving big cuboids will be SOOO much faster now. Wow. I feel stupid.

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Opposite Edge Swap: [R2U2]x3

If you ever complete a layer and find that the middle layers of your right side need to be flipped, you have parity. You need to swap any two identical edges in the layers you're currently solving to fix it [notice the opposite edge swap algorithm has 3 R2 moves, so this will return the right side to normal]. You can do this with some simple setup moves and the edge swap algorithm. For example, U2R2U puts two identical pieces at UF and UB. So U2R2U (setup) + [R2U2]x3 (edge swap) + U'R2U2 (reverse setup) = parity fix. Easy!

This method is nice because it gives you a clear indication when you have parity *before* you get to the end of your solve. You can solve it right then and there before it becomes a problem and involves no additional algorithms, just a setup move. In total, you can do domino solves with only the corner swap and opposite edge swap algorithms = 2 algorithms + some setup moves as needed. Slight modifications of this technique + center solving techniques + edge pairing techniques allow you to solve just about any cuboid and makes parity a breeze. Add in orientation algorithms and you can solve any CUBE, too. Yay!

Wow! I didn't even flip my wife's world upside down when I married her!

The little things make all the difference! I still like your parity fix!

Look at this video
http://www.youtube.com/watch?v=DKObeCvRmHc