Just curious what extensions mean what?
.zbr
.ztl
If there are more than those extensions, please let me know what they are. I thought I saved my 3dmodel but I guess I didnt 
It looks like
.zbr == zbrush format (pixols, only)
.ztl == zbrush tool format (3D objects)
SOmone
You need to save the tool from the " save as " in the tool menu - this way you can import it later for futher manipulation - if you sav as from the document menu you will be saving as a 2d file
hope this helps
a
I guess the export does the same thing, cuz I remember doing both, oh well I was able to save it.
Still learning the program slowly but surely 
maybe I’ll get to the point where I dont make jaggy stuff 
To save or export the pixols on the canvas, use the Document palette. To save or export the 3D object, use the Tool palette.