To upload multiple images to use on products later, choose "Upload Images" from the "My Store" dropdown(shown in red below) or on the home seller area.
The area that appears next should look like the image below and you will want to click "View your Images"(shown in red) to get to the area to upload your pictures.
The next area(shown below) is where you can begin to upload your pictures for your products to use. To upload images, click the upload button(shown in red below) and navigate to your image to upload and click the open button to upload the image. If you want to be organized and efficient for your products, you can click the folder button to the right of the upload button to create folders for each of your products and then put the images in the correct folders.
Now that you're ready to add images to your products, while adding new products, you want to navigate to the "Image" tab to change out default images for your product images.
Once on the images tab, your screen should look like the one below. You need to first change the main product image by clicking on the default image(shown in red below). To add additional images to the product, click on the green plus button and then follow the same steps as changing the main product image.
When you click on the image, you will see a pencil to edit out to the side(shown in red below). To change out the image, click on the pencil and the Image Manager will pop up.
In the Image Manager(shown below), you can select previously uploaded images or view created folders to select images to use. You can also upload images(circled in red) or create folders(circled in blue) while you are in the Image Manager.