Are you using the latest beta of C3 (this is the format it was saved in).
https://editor.construct.net/r325/
can i make a 3d sword so i can pick it up in my right hand and fighting then put it in my inventory.If so how
This is possible, perhaps using enable/disable nodes and creating a model with all the possible inventory options. You can look at the enable/disable node example.
can i make a way so that the so that the ground put the player right where the gorund and the player meet always even in diffrent heights
That requires work outside of 3DObject, I suggest looking at the C3 first person platformer example included in C3 example browser.
