KeepandShare has stored file size limits. So long as you stay within these limits, you can upload any kind of file you like, including video & MP3 files. Of course, video files can be extremely large and can quickly use up your available space. Read Membership Details to understand what the limits are and upgrade your account to higher limits if necessary.
It's easy to upload Video and large MP3 files - you upload them just the same as any PC file - use the Upload Files command.
To see where you stand on stored file limits, click the gray 'Dashboard' tab, then the blue 'Settings' command, then 'View Usage Statistics'. Here you'll find 'Cumulative Disk Space', which details where your account stands against plan limits for shared files regarding monthly bandwidth volume and cumulative disk space.