How much do you know about deepstreamSDK? Please start with deepstream document first. Welcome to the DeepStream Documentation — DeepStream 6.1.1 Release documentation. The basic knowledge of Gstreamer, TensorRT are needed before you start with this document.
DeepStream SDK is just a application level API, for yolov3 model development, you need to refer to https://docs.nvidia.com/metropolis/TLT/tlt-getting-started-guide/.
There is yolov3 sample with deepstream-app, you can read the /opt/nvidia/deepstream/deepstream-5.0/sources/objectDetector_Yolo/README