First thing you need is a modelling app and quite a skill in modelling. If you have no idea on modelling, then it's a long long way of finding the program which suits you the most and learning to use it. At this step you need Poser only for exporting your modelling dummy (the figure clothing is meant for). After the clothing is done, can stop here and import the cloth as dynamic clothing, or go further and rig it to turn it into a conformer.

Since now searching forums is quite easy, you should be able to find dozens of threads starting with same plea as yours, and usually with a bunch of more useful links and/or info than my very basic basics ;)

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