Noob question: What is inside a server? [closed]

There is nothing in a server that couldn't be in desktop hardware (assuming Intel servers.) Some things that are in a server that make it better to provide services 24x7 than desktop hardware:

1. RAID and multiple disks, so that a single disk failure won't take down the server or lose data.
2. Better disks, that can handle more and longer duty
3. Better disks, that can serve data faster
4. Better RAM, that can handle data corruption and fix it with error checking
5. Remote management tools, so you can reboot the machine and get to the BIOS even if you're not in front of it and the OS isn't responding. This also lets you do remote installs of the OS, as you asked.
6. Better (more reliable) hardware in general

Edit- I missed this question : "And how the user interacts with it?" If the "user" is the IT staff that maintains it, they would use remote tools in the OS, or remote management hardware like #5, or KVM units that allow you to hook up a single Keyboard, Video, Mouse combo to many servers and pick which one should be controlled.

If the "user" is not the admin staff, then they interact with whatever the server is serving. If it's an email server, their mail client sends and receives via that server. If it's a web server, the user visits the web page. If it's a database server, the user typically is using an application that is designed to query and/or manipulate that database.

A server is nothing more than a typical computer built to perform better under specific conditions (utilization, environment, performance, reliability, etc) than a typical computer. Typically they have specialized hardware to help accomplish this.

A server rack is a container; it has rails on the four vertical corners to which equipment can be attached. They have common mounting patterns, vertically delineated as Rack Units (1U each). A rackmount server can be installed in one or more of these spaces (some servers take up more than 1U, some less, it depends on the server). Shelves can also be installed to support non-rackmount server.

A blade chassis can be installed in a rack as well. Blade servers are then installed into the blade chassis. Blade servers typically hold more specialized servers. The blade enclosure abstracts certain common hardware from the server and certain external features. Usually this includes power conversion, data buses, internetworking buses, and some management functions.

For more detailed information, please search/ask questions about specific pieces.