To open and close cell groups you want `Shift+Ctrl+{`

and `Shift+Ctrl+}`

respectively.

There are heaps of shortcut keys listed in the documentation:

NotebookShortcuts
and
KeyboardShortcutListing

If you want anything extra, you need to combine the appropriate command or FrontEndToken and put it into the `KeyEventTranslations.tr`

file. This file can be found in

```
FileNameJoin[{$InstallationDirectory, "SystemFiles", "FrontEnd",
"TextResources", "X", "KeyEventTranslations.tr"}]
```

where you replace `"X"`

by the platform you have, either `"X"`

, `"Windows"`

or `"OSX"`

.

For example, a shortcut for moving to the next cell can be implemented by adding

```
Item[KeyEvent["g", Modifiers -> {Control}],
FrontEndExecute[SelectionMove[InputNotebook[], Next, Cell]]]
```

to the `KeyEventTranslations.tr`

.

For more info, here's a SO question on customizing mathematica shortcuts (with good links) and one on adding a key to (un)comment code in Mathematica 7.