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It's in the sidebar to the right.  This is the Properties Output icon. This goes next to "X" and "Y" at the top of the Properties Output Window.  By default, the video output is standard HD (1900 x 1080).  If you want a higher (4K 3840 x 2160) or lower (1280 x 720), you can enter the resolution next in this panel.  The higher the resolution, the longer it will take to render. If you don't see this option in the Properties Output menu, click Dimensions at the top of the panel. Use the menu next to "Frame Rate" to select the frames per second.  30 FPS is standard for film, while 29.97 FPS is standard for YouTube. You can select a number of options between 23.97 FPS, up to 60 FPS.  You can also enter a custom FPS. The menu is below "Output".  Select AVI JPEG to render video in AVI format with each frame compressed using JPEG compression.   AVI RAW will render a video in AVI format with no compression.  This produces large video sizes. You can also select an image format, such as JPEG or PNG and render each frame as a separate image so you can add frames a sequence in a video editor like Adobe Premiere Pro. This prevents you from losing all the frames you've rendered if something goes wrong during the render process. It's in the menu bar in the upper-left corner of Blender 3D. It's the second option in the Render menu.  This begins the process of rendering each frame of the animation.  Be patient.  It can take hours or even days to render a video animation.  You can view the progress in the Render window as it works.
Click the printer icon. Enter the resolution of your video. Select a frame rate. Select a format from the "File Format" menu. Click Render. Click Render Animation.