Get an account at daz3d.com, contentparadise.com, poseraddicts.com, runtimedna.com and shareCG.

Mine the ShareCG, Content Paradise, Poser Addicts, Runtime DNA, DAZ 3D and Renderosity free sections for free props, custom morphs, clothing, characters, hair, etc. Daz 3D and Renderosity have entire forums dedicated to Poser and Daz Studio free stuffs. Generally Poser compatible items are DS compatible as well.

Read the intro to DAZ Studio beginners thread in the Daz forum. Find things that are similar to what you are thinking about and make a list of them in priority.

Then when you decide you need/want to buy stuff, Renderosity, Daz3d, Poser Addicts, Runtime DNA, and Xurge3D are good places to look for fantasy clothing and armor. Xurge is pretty inexpensive and high quality. Renderosity, Daz3d, Poser addicts, and Runtime DNA have a wealth of high quality fantasy items for various figures in various styles. (I make no profit as of yet—I do intend to make something sellable eventually— from any of those sources.)

Tinker with it and figure it out. Don't expect to make what you are meaning for a while.

If you have any specific questions, post a thread here or at DAZ or on one of the other forums something along the line of "newbie needs help with…"