You have a certain amount of storage on our servers in the form of a home folder and a /tmp.
We've built a file browser which you can use to explore your folders, and download any files you've created. Just go to the Dashboard (there's a link at the top right of every page) and then click on the Files tab.
You'll find an "Upload" button appears inside any folders you have write access to. Use this to upload files from your PC.
If you have ssh access (included in all paid-for accounts), you can also use scp (including WinSCP) to copy files up to PythonAnywhere.
From inside the file browser, you can edit text files; find it on the Files tab, then click its "edit" link, and you'll be taken to the file editor. Alternatively, if you prefer to use vim or emacs, you can run them from a bash console.