Aperture (f stop) is the amount the lens is open or closed, more or less light. More so though depth of field (DOF) is greater at a small f stop. Smaller means f/22 whilst a large f stop is f1.4

Landscape shots should be done at smaller apertures to get more of the scene in focus as product shoots and portrait shots are commonly done at larger apertures.

Smaller aperture is a larger number

For video aperture adjusting is in my mind the most important factor. You can set shutter speed and never need to change it, set ISO and never need to change it and rely just wholly on adjusting aperture for your shots.

The principle is pretty simple when looking at the sun or the scene is too light adjust aperture to a greater number (smaller lens opening) to let less light in and darken the scene. Ensure you keep an eye on your focus points though because they will blow out.

Here is a video example (manual focus) from starting at a large and open  aperture f/4 through to the very small and closed aperture of f/22

Going through the f-stops from open to close makes a massive difference to the scene and visuals. Too open (f/4) produces a washed out look and too closed (f/16) makes the footage dark.

Another example from going large to small aperture, note the palm frond tips becoming more defined at a smaller aperture (above f/10)

Images showing aperture change and effects: