From your question, it seems to me like you've already made a 3D model, and you're looking for instructions on how to upload it to ShareCG. Is that correct?

If that's the case, then for a Poser upload you'll need to create a series of folders. (I don't know how DAZ Studio works, I'm sorry.) It should follow the structure of the folders in Poser's runtime, but contain no files except the ones for your model. For example, the folder structure for my last upload looks like this (each folder is inside the previous one):

Runtime, Libraries, Character, cyberwoman, G2F_WorkoutWear

and the actual files are in the "G2F_WorkoutWear" folder. When the content is installed, the new items (in this case a couple items of clothing) will be under the "Figure" catagory, in a folder labeled "cyberwoman" and a subfolder labeled "G2F_WorkoutWear". Does that make sense? Stick a .txt readme in with the folders--I always put it in another folder that also contains the "Runtime" folder--and send the entire bundle to a zip folder. Then you can upload it to ShareCG.

If you're not making content specifically for Poser, I think you can put the .obj file and any associated files (say, texture maps or something like that) in a zip file and upload it to ShareCG's 3D Models section. I'm not certain, though, since so far I've only done Poser stuff. Perhaps you could private message someone who uploads to the 3D Models section frequently and ask how they do it.

If you're looking for recommendations for modeling programs, I model everything in Wings 3D. It takes a little getting used to (what program doesn't?) but I think it works really well if you're willing to experiment with it. I have one tutorial on ShareCG and I'm hoping to make more, but in the mean time I'm always willing to answer questions