Use pre-trained weights from Darknet team. [Not uploaded here due to huge size] Make sure to add the pre-trained weights file to yolo-coco folder before execution.
For image - cd YOLOv3/ python yolo.py --image images/your_image.jpg --yolo yolo-coco (Replace your_image with image name)
For video - cd YOLOv3/ python yolo_video.py --input videos/your_video.mp4 --output output/your_video_output.avi --yolo yolo-coco (Replace your_video and your_video_output with video name)
PS - Adapted from pyimagesearch.com