i am new on auto cad. i want to make a cross section of the two gate witch size is 3 meters and in between there is planter box and there is two steps.

What exactly is your problem?  Do you have a plan view drawn up yet?

YA I HAVE

Do you have any elevations drawn?

YA

Then you should have no problem drawing the cross-section.

No exactly i dont know how i make the cross section ! 

It will depend on where your cut line is located on the plan view.  Everything in front of the line will be shown in elevation.  Everything behind the line will not be shown.

CAN U SEND ME ONE LIKE THIS DESIGN ?IF U DON'T MIND

How about you upload a copy of your drawing instead so we all have a clearer picture of what you are working with?It can be a DWG file and you're limited to a max file size of 500KB.  If the file size is greater than that you'll have to zip the file.
John Connor2013-11-25 14:22:11

YA I WILL USE THE ZIP FILE !

What program are you using?  Is it Civil 3D?

You posted to the Civil 3D forum so are you really using that program or not?  Your profile says Using: self.  Are you self-using?  That could denote any number of weird things.And I thought you were going to provide us with a drawing file.  Where is it?
John Connor2013-11-26 14:19:48