Just place a weapon or what ever on the ground from the entity. Then select that weapon and press "A" to control that objects position vertically. by this u can place that object on the table.
OR
To make it more accurate,...... select that weapon or object then on the right window u can see the entity properties. Here under the position section u can see "Z", where beside that u can see some number like z= 17.62 or what ever. Now by increasing or decreasing that number u can vertically change the position of the object. And after that u can move it on the table..... hope that will do...