I open a lot of separate windows of Chrome on my Mac. However, juggling between two separate windows of Chrome doesn't work with Command+tab. When I press command+tab, only one instance of Chrome can be seen although there are many others in the dock.
Mac apps generally only have one instance, even if they have many separate document windows open. To use the keyboard to switch between windows of the same app, use Command+` (backtick, above the tab key, at least on my US-Qwerty keyboard layout).
I'm not sure what to make of your comment that "there are many others in the dock". Did you make multiple copies of "Google Chrome.app" so you can launch multiple instances, and that's what you see in the dock? It's possible that although you have many copies of Chrome in the dock, maybe you've only actually launched a single instance. Or did you minimize some Chrome windows to the dock, and it's the minimized window icons that you see in the dock that you're thinking are separate instances of Chrome? I think it's probably this.
Swedish keyboard: cmd+<. This should also work for nearly every other application for OS X.
If you have another localisation you could try cmd+"left-bottom-most" key. Hopefully the location is the same.
Applications on Mac OS X are generally only started once, and multiple windows belong to the same process. Internally, there can be additional processes (like for Chrome, or even Safari now), but there is one process responsible for the UI (e.g. the single Dock icon). Workarounds exist, but they are not well known, easy to use, and unreliable.
By clicking a Dock icon or selecting an entry in the application switcher (
To switch to a different window of an application, you can press the keyboard shortcut configured in System Preferences » Keyboard » Keyboard Shortcuts » Keyboard & Text Input:
To go in the reverse direction, additionally press
Another solution for switching between applications and/or windows is Exposé, now in Lion part of Mission Control. You can configure shortcuts for viewing all applications' windows or the current application's windows in *System Preferences » Mission Control:
When invoking the Application windows hotkey (or using the trackpad gesture configured in System Preferences » Trackpad » More Gestures » App Exposé, it presents the application windows side by side, with minimized windows shown smaller below:
There are also third party applications that make window switching easier for users coming from other operating systems, like Witch.