MuSt Help!!!

omg guys, i didnt model so much time and i forgot how to do it.
i downloaded a blp file and as i remmber in the past i added it to my by mpq.
today i tried 2 it, but when i open my map all the units and speels dicontry arent there, just some things that i dont know.
i would thanks if someone can answer me this questin:
1. how i add units(i guess its the blp as i remmber).
2. how i add the speels in this site, i downloaded them but im not sure .
plz help me , i really need it.
3.what is the file mdx?



BTW I KNOW ITS NOT THE RIGHT PLACE TO POST IT AND IM SORRY JUST COULDNT FIND WHERE