Skype is displayed in Default View, with everything in a single window. To resize the window:
You can also switch to Compact View, to view your conversations in separate windows. Click View > Compact View, or click the view button in the top right corner of Skype.
Each window can then be scaled and moved around your screen, so you can organize them in the way that works best for you.
To revert to Default View, click View > Default View, or click on the view button again.