If you can upload then you don't need an account at imgur, but if you want to manage your old images then I guess you will need an account. There should be always an "image file extension" at the end of the link, when you paste the link here. Image file extensions = PNG, JPG, GIF, JPEG, WEBP.... You should not add it by yourself, the image link itself have either one of these.
WebP is a new image format invented by Google. If you convert a regular image to Webp image format, it will reduce its size a lot. So, a web page with webp images can load faster since the page size will be reduced. A memory card/Pen drive can store a lot of image files since the size of the images reduces. WebM is similar file format invented for videos.