The media collections under Resources hold the shared building material: Images, Videos and Documents. Nothing here appears on the site by itself. Products, pages, articles and their sections all point at these, so one upload gets reused everywhere it is needed. Links live in the same sidebar group but are their own thing.
Images accepts any image format and has one field worth caring about: alt text. It is what screen readers announce and what search engines read when the image itself cannot be seen. One short sentence describing what is in the picture is enough. Skip it only for purely decorative graphics.
Every upload field elsewhere in the admin tells you the expected resolution, aspect ratio and format right below the input. Those expectations live with the field, not here, so follow them at the moment of upload. The media guidelines page covers the habit.
Files land in cloud storage and are served through the site's image pipeline, so you never resize anything by hand. Upload the largest sharp version you have and let the site scale it down.
Videos takes MP4 and WebM files only. On upload the system reads the clip's duration and stores it in seconds. You can overwrite the number by hand, and there is one real reason to: carousel slides holding a video stay on screen for exactly this long, so shortening it moves the carousel along earlier.
Documents is the plainest of the three: PDF and ZIP files, nothing to fill in beyond the file itself. Articles use these for their download blocks, spec sheets, manuals, press kits.
Deleting is quiet. Removing an image or video leaves an empty spot wherever it was used, no error, no warning, and there is no usage list to check first. When an asset needs replacing, edit the existing document and swap the file instead of deleting and recreating it. Everything pointing at it comes along for free.