"Daz's Victoria3 and any article of clothing that includes a V3 with the name."...

Umm - that could be unfortunate if it's "Version 3" of a specific bit of clothing....

But what's been said above is correct.

Start with a clean "studio" (IE, delete any figure that's already there, by selecting any part of that figure, then hitting the "Delete" key. Answer appropriately to the following pop-up dialogue (Yes, you DO want to delete the figure).
(The above can be done automatically on start-up, but I'll not go into that just now..1 thing at a time..)

Load V3. With V3 (AKA "Figure 1", usually), selected, do, as suggested above, use the menu bar to turn off what is known as "IK". Click the "Figure" menu, select "Use Inverse Kinematics", click on anything that has a check-mark applied to it. For future reference, the shorthand for explaining this type of action is usually something like: "Go to "Figure->Use IK, and uncheck all".

You'll need to do this procedure twice - once for each leg. The only reason for doing this is to make posing of the figure easier in the initial stages of learning.

Now, in the "characters" library, find some V3 clothing. Click ONCE on an item, just so that it highlights (background turns whiter). At the very bottom of that specific library, there will be two icons (among the rest), one a single checkmark (tick), another a double-checkmark. Click the double-checkmark. This will add the clothing to the scene. (If you get a dialogue along the lines of "Do you want to replace the character"... you've hit the wrong checkmark - or I've mislead you. In either case, hit the other checkmark. There should be no dialogue pop-up).

Ensure that the clothing item is selected (you can check this in various ways, moving the mouse into the preview screen (IE the main Posing screen) should highlight the currently selected item; or check what's selected under the left-most arrow, just above the preview screen. If that still says "Figure 1", then click on the arrow, and select the clothing from the drop-down menu).

Go to menu "Figure->Conform To", and select "Figure 1" (The only choice available, apart from "None"). This will conform the clothing to V3 (=Figure 1).

Add another item (using the double check-mark again - you still don't wan't any "replace" pop-up dialogues). Ensure it is selected (as above). Go to menu "Figure->Conform To", and select "Figure 1" (and NOT whatever you loaded as the previous bit of clotjing - you want V3 to control the movements...)

Now select V3 and pose her. The clothing should follow (more-or-less)...

That's about enough for this mini-tut.

I'm sure it could be expressed more clearly and/or succinctly, but I hope it helps..

Cheers,
Diolma