Amethyst, perfect! I made a screenshot with dictating blue arrows that ought to be sufficient to get you where you need to be. 
Try uploading images this way.
Kinds in Nostr are just the formats you use to publicize things, making it clear what it is supposed to be. In this instance, kind20 is for pictures. This means that apps that are similar to instagram for example (or perhaps somelike like pintrest, or whatever you can imagine that involves pictures), can now find all your pictures based on that kind. At some point in the future when you hopefully start using all sorts of apps it will make sense.
Try uploading images this way.
Kinds in Nostr are just the formats you use to publicize things, making it clear what it is supposed to be. In this instance, kind20 is for pictures. This means that apps that are similar to instagram for example (or perhaps somelike like pintrest, or whatever you can imagine that involves pictures), can now find all your pictures based on that kind. At some point in the future when you hopefully start using all sorts of apps it will make sense.
As for the redering, i.e. 1 picture being horizontal: this is a choice amethyst makes. Other apps might decide to display it completely differently, it is not something you can controll really. Someone could make an app where they would all be spinning around, or display them in some VR gallery as if they are paintings on a wall, or as little portraits inside a clowncar...if that makes any sense.
You are not ON amethyst, you USE amethyst to produce a publication, that can be viewed and commented on with a large variety of apps.
Nostr.