How can I combine multiple textures so that they blend together? I've seen many examples of this, and I can't seem to find the answer anywhere online. The best I've been able to do is, in Texture Paint, edit the actual texture image file.
But what if I could simply unwrap a texture as terrain, and be able to mix, say, a rocky texture with a grassy one, and have one blend into the other smoothly, rather than an abrupt edge?
I've seen this executed beautifully before, and if anyone could give me any insights, I'd really appreciate it! I feel like it's the missing piece that would improve my creations.
The traditional way to do this was vertex colors. The amount of (say) red would be the blend factor between the textures. Use a node setup like this.

Set the 3D View to Material preview and switch to Vertex Paint mode. Paint black where you want the first texture to show through, and red where you want the second.

Alternatively, you could use a third texture to control the blend amount and paint it in Texture Paint mode.