For training I'd start with the latest videos from renderosity on you tube.

https://www.youtube.com/playlist?list=PLHskz2PNix3Alw_gLu1_ezbQGg7kqUFVZ

Once you get started with the free content then you will probably get to the stage of deciding you need a specific item to complete a scene the way you want, then people here will be able to come up with specific suggestions.

Do you have a favourite genre or know what type of renders you are hoping to create, portraits, outdoors scenes, crowded indoor scenes? Poser is so versatile it's difficult to give general ideas