ok well first thing you need to do is make sure the object download is in my_objects.
heres step by step instructions on how:
1) open object maker
2) go to the second panel
3) in the mesh bar type in the mesh file (example: tree.mesh)
4) click "add new"
5) the object should appear
6) go back to the first panel
7) type in the name of the object and the group it should go into

click save
9) then you have your object!