Do you mean to your wordpress.com blog or to another install on another host? There is no 'uploading' tool for a gallery on wordpress.com hosted blogs except adding them one by one through the create post interface or linking to other online galleries such as flickr or imagecaddy. If you want videos, google video and youtube also integrate nicely, but if you have the "space upgrade" there is also the wordpress.com video player.
None of these are really important if you have a blog not on wordpress.com since you can upload plugins on other installs and should be at http://wordpress.org/support/ for that.
Let us know where the blog is located for more specific instructions if it is on wordpress.com.