Most newer photographers will begin their editing journey in Lightroom rather than Photoshop, and even as you become more advanced, you will notice that you can still do a lot or even most of your editing in the former, only needing to resort to the latter for truly complex post-processing tasks. If you are a beginner and looking to understand how the various editing functions in Lightroom work, check out this great video tutorial that will have you up and running in no time at all.
Coming to you from Anthony Morganti, this excellent video tutorial will show you the basics of editing a photo using Lightroom. If you are new to post-processing, the most important thing to remember is to use a lighter touch than you think you need. It is tempting to crank sliders like saturation and contrast way up, but this can often lead to a photo looking overly artificial or garish. It is easy to get a bit of tunnel vision during an edit, so one of the best habits you can get into is to step away from your computer when you are done with a set of images, give your eyes a few minutes to reset, then return to evaluate the batch one more time before you export them. You'll often find you'll want to dial things back just a bit at that point. Check out the video above for the full rundown from Morganti.
I have used Photoshops ACR for years and find it is lightyears easier to edit than Lightroom. I find Lightroom to be tedious and difficult. My choice is always ACR first and why go to Lightroom if I can do the same thing in ACR?