Trim, cut and join clips, then save a real MP4 — all on your own machine
For most of the medium's history, cutting film meant a room full of equipment and, later, a desktop application heavy enough to need its own machine. What changed is not that video became simpler but that the ordinary browser grew the parts a cutting room needs: it can now decode a moving picture, hand the individual frames to a page, and compress new ones back into a standard file. A trim that once meant installing software and waiting for an upload is now a page you open and close.
The vocabulary is worth knowing, because it is the same everywhere. Resolution counts the lines in the picture — 1080p, 1440p, 4K — and governs how much detail survives. Aspect ratio is the shape of the frame, and it is a stronger choice than it looks: 16:9 is the shape of televisions and most of the web, 9:16 belongs to the phone held upright, 21:9 is the wide cinema frame, 4:3 is the shape of everything shot before the mid-2000s, and 1:1 is the square that social feeds settled on. Putting a shot into a frame it was not filmed for means either accepting bars along two edges or cropping away part of the image, and there is no third answer.
Two habits save more trouble than any tool. Cut for the audience rather than for the footage: the interesting part almost always starts later and ends earlier than the raw clip does, and a ruthless trim is usually the single biggest improvement available. And decide the destination before exporting rather than after, because every platform has a shape and a size it prefers, and a file made for the wrong one gets re-compressed on arrival — which is where sharp footage quietly turns soft.