This it what the MediaPanel looks like when opened for the first time. You can upload new files with the '+' button.
Then this window pops up. Select 'browse files' to open the corresponding dialogue.
Choose the file you want to upload and click 'open' (you can upload up to 10 files at once by holding the Ctrl-key while selecting).
The progress bar shows the upload progress, a yellow star-icon will appear when completed. Select 'close' to transfer the uploaded file(s) to the MediaPanel.
The new files are shown in the MediaPanel. Put them on your page by clicking and dragging the files. To delete a file, select it and press the '-' button.