To buy things on Renderosity you register a user name, which you have already done seeing that you are posting here.

You click on the link "Market Place" at the very top of the page. 

When you find something you want to buy, add it to your shopping cart.

When you are finished shopping, go through the checkout.

You can pay by PayPal, or credit card.

If it's your first time buying something here then you will not be able to instantly download.  You will get an email asking for a verification.  Follow the instructions in the email, and once you have done the verification, and the store staff have verified the information, your  purchase will be given a download link for you  to use.  Any future purchases after that will be get an instant download button.

Hope that helps.

One thing to add..... when you are buying something, make sure you aren't buying a texture for something you don't own.  Textures are item/figure specific, so if you buy a texture for a dress, it won't just fit any dress, you need to own the dress that the texture is for.

And if you want to use the character addons for a figure you need to make sure you have the head and body morphs for that figure too, otherwise you won't be able to use the morphs, just the textures.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi