There are a few ways to upload photos - directly on the pages/e-commerce item you are editing, or from the Photos menu.

From the page itself:

...On the Add/Edit Page, from the left side column, next to the Page Content box:

You can add/manage photos directly from the Add/Edit Page. Just click on the "+ Add Photo(s) link to upload". Plus, you can choose to “assign” photos to a specific page for quick access to the photo on that specific page, or leave it unassigned to any pages so that the photo is available for quick access on all the add/edit pages.

For Slideshows and Galleries that display on your page, you will want to create/manage your photo categories.

When creating a new page, you can just checkmark the box for “Create new Photo Category for page” next to the Content Page Editor Box and click the button at the bottom of the page to add the page/save the page updates.

On the Edit Page, to go to the photo category/categories of a page, to upload photos for your photo gallery/slideshow, there is a Photo Categories link/count to easily view/manage Photo Categories associated with a page.

...On the Add/Edit Item page:

Add/manage item photos directly from the Add/Edit Item page, besides on the Admin Panel Photos section. Similar to the Add/Edit pages. Untag a photo to the item to not associate it with the item.

From the Photos menu:

To upload photos to your website, from the top menu bar go to the Photos > Add Photo tab.  

On the Add Photo page, choose either a Photo Category to add the photo(s) to, or a Page.  You can also tag a photo to an e-commerce item, by choosing the item name from the Tag To Item drop down menu here.

To create a photo category first, from the top menu bar go to the Photos > Add Category tab. 

Photos that are added to a Photo Category are used for the Photo section of a page, and also for photo galleries/slideshows (refer to Adding Photos / Slideshows / Photo Galleries To Page Photo Section). 

Photos that are added to a page (called Inline Photos) may be added to the text section of a page on the add/edit page - they are listed on the left side column of the text editor section (refer to Adding Inline Photos).