How do you upload and save a DVD to your computer?
To make a backup of a DVD you own (to be able to play it on different devices, etc..) you must use a computer program that reads the disk, and stores it in a file format with high quality.
There are many such programs, a free one that is widely used is in a link below.
For free DVD Ripper software, Handbrake will be a good idea if you just rip DVDs now and then or have no special requirements like editing, adjust parameter for DVD Movies.
Most commercial DVDs have copy protection to prevent the content being stored elsewhere. The owners of the content use this to protect their investment into the work. Please respect the copyright on all work and remember that in some jurisdictions, making or distributing copies of copyright work is not only a civil offence but criminal as well.
Unless you have the computers networked, you can't. You'd have to save the slide show on a flash drive or other writable media (such as a DVD) and bring the device to the friend's computer in order to watch it. Alternately, you could upload the slide show to the Internet from your computer and download it on your friend's computer.