Textures would need to be done in either a 2D paint program or a 3D painting program and then they would have to be set up in DS or Poser. You can't actually create textures in either program but you can set up a materials network in both.
So I found this a little confusing, because I think of the Texture as being synonymous with the Material, and maybe they are not. The truth is I've always found the terminology around materials confusing, and it's made it hard for me to figure out a lot of things, so I thought I'd define how I understand these terms. If I'm wrong please let me know.
UV - when you model a 3d item a UV of some sort is created. Sometimes usable, sometimes not. Basically the modeler tries to figure out if you flattened out (or unwrapped) the 3d object, where would everything be on a 2d plane with U and V coordinates not X and Y. The UV itself is stored in the geometry files.
UV Layout - This is in essence the 2d representation of the surface of the 3d object. Basically the map vs. the globe. It's not actually part of the geometry files, but a separate file you need to use a program to create, that helps you color in the object. Many products come with a Template folder, and these are basically the UV Layouts of the object. However you do not need a UV layout for your object to have color, texture, etc.
Image Map - This is a pretty broad term. And can be a lot of things. Many materials/textures are made up of many image maps. They are .jpg or .png and what I think Pendraia meant by texture. When you take a UV layout of say a shirt, and paint buttons on it in a program like Photoshop, you are creating an image map that can be used in Poser/DS so that it looks like your shirt has buttons, even if you never modeled them on. Other common image maps are bump/normal/displacement maps which trick the 3d program into adding texture (in the sense of, "Oh that looks like it has a rough texture. I bet it would be bumpy if I touched it" as opposed to something that looks smooth). Also things like transparency maps are image maps.
Nodes/Bricks - Poser uses Nodes, DS uses Bricks. They are basically the same thing. These are how you load up image maps, decide whether they are to be used to color the object, or as a bump map etc. and add in all kinds of other effects like specular, diffuse, and so on to 'color in' your 3d object. When you have put together a bunch of nodes/bricks, you have made a material.
Materials/Shaders - Some 3d programs like therm Material, some like the term Shader. They are basically the same thing, they are the what you choose in your library to change the color and look of an object. Some are really complex, some are simple. They are as I said put together with a bunch of nodes/bricks and the material gives the final look to your object.
Procedural Nodes (bricks?) - Okay, I don't know DS well enough to know if it has procedural bricks, but I'm assuming it does. In case it doesn't I'll just talk about procedural nodes here. This is actually the whole reason why I found Pendraia's comment confusing at first. Procedural nodes are a way to alter a material so that either you don't need image maps, or to alter them. For instance, you don't actually need to make a bump map for a clothing item. Poser has procedural nodes that will add a weave pattern for you. It has others that will randomize and alter the look of something in all sorts of ways. Now there isn't a 'add buttons to my shirt' procedural node, so you would need to use an image map there. But there are ones to make bricks, waves, scales. For instance the second image Pen posted above, could probably be made entirely using procedural nodes in Poser. The down side to procedurals is that they are not at all compatible between programs. So you can take an image map, and use it in both, but you can rarely do that with a procedural node. You need to figure out a different way to simulate it in the other program.
Material Groups - These are the different areas of an object that have different materials applied to them. So for instance you might have the trim separate from the main fabric of a an outfit. Or looking at the example Pen used, I would say there are two different belt groups on her skirt, so she can either have them match, or be different.
Like I said, if anyone disagrees with any of my definitions let me know, but this was something that confused me early on, and I wish I had found something like this that had lots of definitions, so that I could better learn and search for what I needed at various points.