I would love to get into photography, but I have no clue about cameras whatsoever. All the pictures that I currently shoot are made with my Google Pixel, which definitely takes nice images. But I want to step up and get myself a real camera.
Any used DSLR or large sensor mirrorless camera would be fine for any general photography introduction. Specifically, if you want to learn to use ISO and aperture values a larger sensor is important, as aperture has little effect in smaller sensor devices ( phones, tablets, most point and shoot cameras ), but is much more significant with large sensor devices.
Do not get distracted by megapixel counts. It's not so long ago that a 6Mp image from a DSLR taken by a pro would have been happily used in a full page magazine spread. I still have large prints on my walls that came from a 6Mp DSLR and kit lens ( mine, of course ).
Starting out a basic kit lens ( like an 18-55 ) is fine. They're actually pretty good lenses optically nowadays, and well suited to introductory landscape shooting.
The temptation to buy accessories and more lenses is normal. Resist it, as you'll most likely be wasting money until you have a solid understanding of your basic kit. Resist the temptation to blame the equipment for your problems in your photos - look for problems in your technique instead. Experience has taught me that it's usually my technique that messes up a shot and not my equipment.
Types of cameras that will work
For landscape photography, specifically, nearly any current digital camera--including those on smartphones--can do a good job. What you really need to worry about more is getting a tripod to use with it, and learning proper landscape photography technique, which generally involves using smaller apertures for a deeper depth of field, and reducing vibration for longer exposures (cable release, timer, etc.)
Camera specs to look for
What you'll want to look for are dynamic range capabilities, and resolution. And the resolution you choose should match the output format you plan to use. If you're only going to post online or send image around in emails, again, nearly any current digital camera will do. It's when you want to make big gallery prints, that you need to consider how many megapixels the sensor produces.
Features to look for
Personally, the only two features you probably really need to look for are full Manual shooting mode, so you can control the exposure settings explicitly. M mode generally comes with with what are known as the "PSAM" modes (Programmable Auto, Shutter-priority, Aperture-priority, and Manual). And you probably want RAW capability, if you plan to do your own post-processing to get the most out of the digital data. RAW lets you bypass JPEG compression if you want to.
Many people prefer a wider lens for shooting landscapes, but it's not a requirement--some folks shoot landscapes with tele lenses, too. But if you're getting a compact fixed-lens camera, 24mm film-equivalence (vs. 28mm or 35mm) may make you happier if you like shooting wide.
A final note on budget
For $400, I honestly wouldn't recommend going for an interchangeable lens solution, because you may only be able to afford the camera body, and not lenses to accompany it. For $500 and below budgets, I'd recommend a fixed-lens camera, and you may have to go used or lower-end if that budget also has to include a tripod of some kind. But with a smaller lighter camera, you could probably get away with a smaller travel tripod or evey something like a gorillapod or beanbag.
I have never used a Nikon or Canon DSLR so I will not attempt to compare what I am used to to one of those cameras which I am sure are fine, but I have never used.
I started out with a Ricoh film SLR in 1986 and had no mentors so I just took what the salesman told me and started teaching myself. I had two lenses, 35mm-70mm zoom and a 70mm-210mm telephoto zoom. There was no autofocus and my only "auto" type features were Aperture Priority and Shutter Priority. My learning curve was slow.
Now enter the digital age. Today Ricoh is the parent company of Pentax and they share a lens mount, commonly referred to as the "K-mount". They have always been backward compatible with the K-mount lenses of the past. This avails you of many older but superb lenses as you move forward in your learning. As someone else did mention, concentrate on a basic lens that comes with your camera and don't start buying different lenses until you master the basics of your new SLR camera.
Another feature of the Pentax line of cameras is the image stabilization technology that other manufacturers put into their lenses, Pentax has incorporated into their camera bodies. This means that a 25 year old K-mount lens can take advantage of that modern technology. Once again this opens you up to a host of older lenses that you can use.
As for what model, the K50 is a good entry level camera and in kit form (with a lens, 18mm - 55mm zoom lens) is around $475 on Amazon. It is a 16mp weather sealed camera that can run from fully automatic to fully manual and all points in between. It has a fairly high ISO capability (51200) that will enable very low light photos although I would probably stay below that setting myself.
Most any entry level camera you wind up purchasing will be easy to setup and get started using.
I hope this information helps you to make a good decision when you go to make your purchase.
I would recommend a Nikon D3300 or D3400, both of these cameras are simple to set up and use. They are both very high quality and take very good quality pictures. You can choose to do things automatically where the camera sets everything up for you, have certain parts auto and others manual or you can do everything manually.
