In order to obtain a SWEM horse, the player needs Cantazarite. Its ore is found underground or in the mountains, and once mined it can be used to brew a Cantazarite Potion. This potion is then used on vanilla horses by right clicking them, turning them into SWEM horses.
SWEM horses cannot be ridden without certain tack. A bridle, saddle blanket, saddle, and girth strap are necessary to control and stay on the horse, although there are many other pieces of optional tack. Most are crafted with refined leather among other items.
In the plains biome, broken-down farm structures spawn on occasion. These come with a house, a few stalls, and a small barn with barrels containing different SWEM items. These items include shavings, bandages, salve, rubber mats, glistening melons, friendly bars, and hitching posts. The structure also includes a well and a small plot growing wheat, oats, timothy grass, and alfalfa. The latter three are used in crafting quality bales and sweet feed for feeding horses.
This structure is especially helpful for a starter home. With a little TLC, it makes a nice house to get started in your journey.