There is a way to open a file dialog window to pick a file. For such switch to NORMAL by pressing:

<Escape>

Then press:

<Key-C>

It will open a file dialog window in which you can select a file to be edited.

There is a handy keycommand to save file changes. Open an existing file, switch to INSERT mode by pressing:

<Key-i>

Insert some lines. Switch to NORMAL mode by pressing:

<Escape>

Then press:

<Control-s>

In case of failure or success a msg would appear on the statusbar.

It is possible to save a file with a new name by opening a save as dialog window. Switch to NORMAL mode then press:

<Shift-s>