Source

Choose what to render and how long.

Range — the time span: Custom (a start/end you set), Loop (the timeline's loop range), Soundtrack (the main soundtrack's length), or Continuous (keep recording until you press stop — great for live sets).
Scale — whether Start/End are in musical bars, seconds, or frames.
FPS — frames per second of the output (60 is a good default).
Resolution Scale — a multiplier on the output size. Set it to 2 for 4K from a 1080p comp.
Motion Blur — only for projects using [RenderWithMotionBlur]; overrides its quality just for the export.

Hover the (?) next to any field for a short explanation. Click below for the full guide.