mmmk when I was doing my first map I had the same trouble ok open up the zip. file select all of the files right click copy then go to local disk> Feralheart> media> objects>myobjects then paste them all there. Open up the game and go to object maker ok now all you have to do is go to the tab that says mesh then type in the mesh file you want to use in the mesh spot then click add new then go to the object tab and type in the name you wish to name your object then make a new group name it whatever you want then press save. For example if I wanted to add some leaves that were in the wombat foliage pack I would type in leaves.mesh in the mesh spot then go to the object tab and create a new group then name the object then create a new group saying Leaves then press save then I would go to map maker and ta da your group is there click that group and you will see the mesh you have just imported. Hope this helps.
