linux mint 18.3 sudo problems

I've just installed linux mint 18.3. I have a problem that I can't access files where I am user when I am sudo in the terminal. I have backed up program lists that need to be installed as sudo as well as new downloads to install that can't be done as the directories can neither be located nor created. I just get the message that they can not be found. The only thing I can see from the terminal is Desktop.