I am new to this as well, So I think I may be able to guess your concerns better then someone who has used linux for years. I just started using linux, I use a Debian based one (Debian has good support). The differences you will notice are:
1) CONTROL - Windows may let you change themes, drag files, and edit password but linux can be 100% changed by your actions. You can configure the whole thing and even create you own OS if you know what you are doing (They even include a license within linux for you to legally remake any part and distribute it). you can still do things in a fashion like windows (Such as drag a file to a new location,right click for a menu of options, etc) but it is more detailed.
2) SUPPORT - When you call windows customer service (As I had to do when my XP crashed) you get put on hold, then get some twit for a cust. rep. whose job is to find out your problem, and charge to fix it. With Linux you get IRC channels for direct help, and a variety of forums (I like this one lol) with knowledgeable people to assist you, given you know the nature of your problem. and even if you don't I've seen these guys work miracles (Q:I got grilled cheese in my processor, is that a problem?'' A: ''just type in the terminal: $ cheese -wipe/clean'') and have spent time reading the forums just to anticipate any problems I may get.
3)RELIABILITY- Windows crashes, has auto updates that could do more damage then good, and if you want to try another version of windows, it's $100 to do it. Linux is used for Macs, smartphones, laptops,pc, and netbooks (due to it's versitility and small size of some versions it can be installed with low disk usage almost anywhere) and is good to go right away, and may crash if you edit things, but you can just reboot and either re-install or load your own GRUB setting and get your desktop right back.
Overall I am not that great with linux, I am still learning the commands for the terminal (The terminal works pretty much like DOS does in windows, it interacts with the shell which is essentially the nervous system of your computer. if it is the nervous system; you are the brain, You tell it a command, and it reacts. If something will not work it will tell you what and why... Most of the time anyways.) and still learning where stuff goes. but it is faster,smoother, and in the long run easier to use then windows (IE windows says ERROR-290838420935 XKJ 0920934 wereas linux says ERROR - You have not installed that driver, Search for it now?) even though it takes a bit more work. If you want it to behave like windows here is a Linux system built on Ubuntu which is well known and supported, and this one looks and acts like windows so you can transition easily.
Best of luck!