Press Win-C (for "charms") to open the charms bar no matter what system context you're in. The resulting menu can be browsed by using the arrow keys and Enter. (Click for larger version.)
Knowing when to go MetroMetro's interface isn't its only thing facet. The way apps work under Metro is also significant -- so much so that Microsoft engineered an app-development platform and design language around it, WinRT (not to be confused with the Windows RT version of Windows 8 for ARM tablets that prvides the Metro environment and just special versions of the Windows Desktop's Office 2013 and Internet Explorer 10).
The Metro model works best for apps geared toward information consumption -- what some have called "lean-back mode" -- or where interaction is reduced to a few simple gestures. A Metro video playback app is going to be more useful than, say, a Metro-based text editor. On the other hand, a Metro Twitter client might be a good compromise; you'd still need to type, but not as much.
Most of the apps designed for Metro are content consumption apps or apps designed for simple interactivity, such as games. (Click for larger version.)
As a result, you're best off not trying to replace existing desktop apps with Metro apps, except for desktop apps primarily designed for consumption. Don't expect every single app, or every single kind of app, to turn up in a Metro incarnation -- at least not at first, and not until Windows users are comfortable enough with Metro to attempt working with more sophisticated apps.
One example of a good replacement app would be the Metro Kindle app. It's slightly easier to deal with via a touchscreen device than the legacy/desktop Kindle app, and its power consumption optimization will stand you in better stead if you're taking your Windows 8 machine with you.
A good example of a Metro app that works as a suitable replacement for a desktop app: Amazon Kindle. (Click for larger version.)
Mitigating the misery of multiple monitorsBecause it is aimed squarely at slates and notebooks, Windows 8 doesn't handle multiple monitors well.