how do I add Paypal/shopping cart to my blog please

Hi

I would like to offer parents the opportunity to buy prints from their portrait session directly from my blog.

I have set up a button in paypal, but do not know how to add it to my blog.

The only form I have is a contact form, I can’t find any others.

I want to be able for them to input (manually) a photo id number, then select if they want gloss or matt, then choose from a number of sizes.

But I really can’t get my head round it. I can’t add plugin’s, I thought upgrading would allow me to, it didn’t so I cancelled the upgrade.

I am possibly being really stupid and the way is very simple/straight forward, I am pc literate, I really don’t know why I’m struggling with it.

If you need to see my site or look at the techie side of it, to see how best I add it, its https://www.dualfocusphotography.com.

Thank you I look forward to hearing from you (with a huge sigh of relief I am certain).

Clair