If you open File Manager and go all the way to the top you will see some folder that has the same name as you called your N900 device. This is the /home/user/MyDocs folder, so if you save the file to this folder, then open the terminal and:
cd /home/user/MyDocs
If you have a MicroSD card in there and you saved it to it, it should be automatically mounted somewhere in /media/ so you can cd there...