This is a very basic, but very necessary read for understanding the command line utility Terminal in OS X. Its short, sweet, and very informative. Give it a read.
http://blog.teamtreehouse.com/introduction-to-the-mac-os-x-command-line
Here is a basic cheat sheet of every basic command line parameter known with a description of what they do. It has all the ones you'll use the most, and a few that can get you into trouble. Use it mainly as a reference sheet.
https://github.com/0nn0/terminal-mac-cheatsheet/wiki/Terminal-Cheatsheet-for-Mac-(-basics-)
Finally, here is a complete A-Z list of every known OS X command line parameters, including the Unix shell in-built commands. Its a very comprehensive list with descriptions. A lot of these can get you into trouble if you use them incorrectly. Use this ONLY as a reference for when you see something you want to try but don't know what it does. (IE: Changing a users password with the passwd command.)
http://ss64.com/osx/
Knowing the command line extensively isnt required. Knowing how to use it proficiently isn't required but it will eventually help. You'll google an issue and someone will give you a command to enter into Terminal, and if you have no idea even how to get to Terminal, you're going to be head scratching and a little miffed.
As a beginner, I started with beginner things. Get comfortable navigating a folder structure inside Terminal. Changing directories can be quite a challenge, especially if you're stuck in single-user mode and do not have a GUI to help you navigate. Understand that you can jump from folder to folder without actually navigating through all the folders to get to the one you want. (Going to users > username > Documents > My stuff. You can actually go from any other folder DIRECTLY to that folder!)
Once you get that down, get comfortable copying/moving files and folders. This in particular can be a time saver. Once you understand the 'mv' and 'copy' commands, you can literally move millions of folders/files scattered almost anywhere in a few simple keyboard strokes. Much easier than hunting them down individually.
Finally, get to know some of the more advanced parameters. These are almost never used by most regular users. I use them quite often though. A lot of hidden settings for OS X are in these parameters. I'd tend to stay away from them unless you know what they're going to do.
To be honest, I'd put command line on the back burner for now and get to know how to troubleshoot your Mac. As an experienced Windows user, I'm sure you are used to troubleshooting your Windows PC's from time to time when they started to slow down. Mac's are no different and they will eventually need to be tinkered with. I'll give you a few OS X alternatives to the usual Windows counterparts.
Console: Task Manager for OS X. From here, you can kill a process job, view CPU usage, RAM usage, network bandwidth usage, etc.
Force Quit: More Task Manager related. It lets you quickly force quit a stuck application. Even has its own "Three-finger salute". (Command-Option-Escape)
Disk Utility: Not much like it on Windows. It allows you to format memory sticks, burn CD/DVD's, and much more advanced items. Depending on your version of OS X, you may use this frequently to repair permissions.
System Preferences: Control Panel for OS X. Inside here, you'll find a tab called "Accounts". Click your account name and then select "Start Up". This is "MSCONFIG" for OS X. Use this to deselect any applications that start with OS X.
All of these are very well documented online by Apple, so if you ever get stuck with something, answers are readily available.
Finally, welcome to OS X. I hope you enjoy your switch! It won't be long before you'll wonder why you stuck with Microsoft for so long.
