Instagram and Me

I am going to try and use Instagram to post photographs of my paintings and my blog.  Everyone says it's a great way to Showcase my work.  Now I have to figure out how to use it.  I don't have an iPhone, just an iPad and I'd like to take the photos of my paintings from there.  Have to make sure all paintings are Watermarked.  Might have to take another trip to the Apple Store for some help.  What I really need is a younger person to teach me how to do all this "new" stuff!!!!  Does anyone know how to get photos from a Mac Desktop or an iPad to Instagram?