sorry for posting the wrong link
http://wiki.minetest.net/Installing_Mods is the wiki page I wantedt to link to.
as far as I can see the correct path for your system would be:
/usr/share/games/minetest/
mods/carts/if you do not have a mods folder in that position create it.
rename PilzAdam-carts-10c4557 to
cartsonce done do as the wiki says
http://wiki.minetest.net wrote:After extracting the mod there you need to enable it for your world. This can either be done in the GUI by clicking on “Configure” in the world selection, or by adding load_mod_<modname> = true in the world.mt file in the world directory.
Note that new installed mods are disabled for all worlds by default, so you explicitly need to enable them.