Uploading pictures
Getting images in, and where they live afterwards.
Media in the sidebar is every picture on your site in one place. Drag files onto the dotted area, or press Upload.
You can also add a picture from inside an entry — any field marked as an image will offer to choose one or upload a new one. Either way it lands in the same library, so a photo uploaded while writing a page is available everywhere afterwards.
Sizes
Upload the biggest version you have; you cannot add detail later. Around 1600 pixels across suits most wide images. There is an upload size limit — usually 25 megabytes — and you will be told plainly if you exceed it.
Inkling reads each picture's dimensions as it arrives, which is what lets your website lay pages out without the text jumping about as images load.
Folders
You can put pictures in folders and filter by them. Worth doing once you pass fifty or so; not worth doing before.