Uploading image files is one of the core features for the Store Admin.
All you need to start uploading images is an event. If you wanted to organise the event using albums, it can be a good idea to create them first as well.
Once an event has been created, you can click the Upload button on the event itself or from the left-hand side menu.
The upload will page will show all the albums for the event. To start the upload click the "Upload from your Computer" button next to "Uncategorised" or the album you want to upload into.
Next, you will be asked to select the files you want to upload into the album. To make this process quick, you can select multiple files one go using your mouse or keyboard. The Ctrl-A keyboard shortcut will select all the files in the current folder.
Once the files have been selected simply click "Start Upload" to commence the upload. The page will show all the selected files and provide an upload progress indicator.
Important note: Don't close this window until all the files have been uploaded.