I am new to non-auto mode.
If I have a fixed aperture lens with f/2.8 16–35 mm. Does this mean I cannot change the aperture to f/4 or f/5 on my camera because the lens only supports f/2.8?
Is the f/2.8 of the lens independent and separate from what the camera can vary f to?
The f/2.8 in the name of the lens does not indicate fixed aperture in the sense of not being able to change it - it designates the widest aperture. You should still be able to set it to e.g. f/4 or f/8, but you won't be able to set it to f/2, because the maximum is f/2.8.
The sense in which it is "fixed" is that you can use f/2.8 throughout the zoom range, as opposed to a lens that has a different maximum aperture at each end of the range, like a 70-300mm f/4-5.6 lens - that has f/4 at the 70mm end and f/5.6 at the 300mm end. It's more often referred to as "constant" aperture, not "fixed".
If a lens has a fixed aperture you cannot change it. But such lenses aren't very common for interchangeable lens cameras. The most common lens of this type would be a "mirror lens", and these are usually fixed at f/5.6 or f/8 for focal lengths around 500-800mm.
If your lens has a maximum aperture of f/2.8, you almost certainly have a constant aperture zoom lens that is capable of maintaining the same maximum aperture (minimum f-number) throughout its focal length range. Constant aperture lenses can be stopped down. The numbers in the model names indicate the maximum size of the opening, not the only size of the opening.
If there is no aperture ring on the lens that just means you must use the camera's controls to change the size of the aperture in the lens at the instant of exposure. No matter what aperture you or the camera select for exposure, the lens normally stays wide open until the instant before the picture is taken. This allows for a brighter viewfinder and more sensitive and accurate autofocusing.
The terminology in your question is most likely incorrect.
Several manufacturers make a 16-35mm F/2.8 lens which is a Constant-Aperture Zoom meaning that its has the same maximum aperture at any focal-length. This means you can set it to F/2.8 at 16mm and 35mm or any focal-length in between. You can also stop it down at any focal-length. Most, if not all, constant-aperture zooms have the same minimum aperture throughout the zoom range which is nearly always F/22. Any combination of focal-length from 16 to 35mm and aperture from F/2.8 to F/22 is selectable.
Other types of lenses are:
Yes, on your lens you will have the full range, from f2.8 and up, at all focal lengths.
