New to streaming? Check out the Official OBS Quick Start Guide first!
Firstly, make sure you have created a scene and added a source (right click the sources box). After that, you'll need to turn on 'Preview Stream' or be streaming / recording in order to see your stream
If you use a laptop, you may have a black screen due to switchable graphics. See this thread for more information.
You need to be previewing your stream, or actually streaming and click 'Edit Scene' to move things around. You can also hold Ctrl while moving a source to prevent it from snapping to the screen edges, Shift while resizing to ignore the aspect ratio, and Alt while dragging the edge of a source to crop.
Are you trying to stream a fullscreen game? You'll need to hook into it using the 'Game Capture' source in OBS. As well, OpenGL games like Minecraft have issues with Window Capture and you'll need to use Monitor Capture to show them. If desktop capture is showing up as black, it indicates that you either need to update windows or update DirectX.
This is usually caused by poor network connectivity to the streaming server, or an overworked CPU. If your "Dropped Frames" counter in OBS is higher than 0, see this thread for advice on fixing network issues. Otherwise, see this thread for advice on fixing overloaded CPU issues.
Make sure you have the latest version of DirectX and that your video card drivers are up to date.
If you continue to receive this error even after installing DirectX, you could try using DXFix.
Your capture device may still be unsupported -- please visit the forum and read the thread regarding red output from devices. Note that some device manufacturers do not provide 64 bit drivers, so make sure you are running the 32 bit version of OBS for maximum compatibility.
Check out our settings estimator for general recommendations based on your setup
Windows XP unfortunately lacks DirectX 10 features and the audio subsystem present in Vista and up that OBS makes use of, and as such, will never be supported. OBS is currently being rewritten as multiplatform under the name OBS Studio. It will be available for Windows, Mac and Linux when it is done.