addons from a server

is there any thing to open or use dua or is there a way to use them in when not on the server you got them from

You can open them with any text editor.

can you use it to covert it into normal lua to use it in one player

The dua folder only contains client side lua, so unless they had all of the files in shared then it will not work. So chances are it wont work no.

put on your reading glasses, here comes the wall of text:

step 1: Rename file to .lua
step 2: Put in appropriate folder.