Everybody started sometime, you will pick it up.

In Poser if you switch to the material room and the advanced tab you will see a set of parameters for that material .

You can select the material by clicking on the small preview image , or using the pulldown list near the top.

Diffuse in the PoserSurface node (should be far left of the screen) lets you change the color if there is no image map. So if you have a white robe, changing diffuse colr to blue will give you a blue robe.

Its often better to make a new texture image by ussing the product template or uv map.

There should be a section in the manual on the material room. Ask in the Poser forum for help. 

changing an items materials is done all the time in Poser. You can have one dress and make it look like lots of different dresses with textures and transparency maps.

You may find some tutorials as well on renderosity.