You don't need any linux knowledge to do normal stuff on the tablet. It helps to know a few things, but not at all necessary. For a newbie, all the basics Just Work, and you should find good instructions here and on the wiki to install most any program you need.

The Hildon framework used on Maemo is actually a part of GNOME, consisting of some GTK extensions, and IMO much better for a tablet than general purpose environment. You can recompile many GTK apps for the N810 with not a whole lot of effort.

For taking notes, any lightweight text editor will do, like the built in one or leafpad, although you might find the bluetooth delay annoying if you type fast. OO.org and Abiword are overkill, although nice to have for opening MS formatted files.

If you have a desktop, the best way to learn linux would be to install Ubuntu or similar on it and just play with it.