Ever have a bunch of files you want to rename? Maybe you received a group of documents from your Windows-using friend that have some wonky text in them, or maybe you want to serialize and date some pictures? Automator, built right into your Mac, makes this so easy you'll scratch your head twice; once for not having done this with Automator in the past, and a second time if you've never used Automator before because you'll see how easy and powerful it is.
Step 1: Launch Automator (in your Applications folder) and choose to create a new Workflow (depending on whether and how you've used Automator in the past you might have to choose "New" from the File menu, or it might just come up and ask you what to do).
Step 2: In Automator's "Library" click on "Files & Folders." That will narrow down the view showing you all the available actions pertaining to the Finder. You're going to use but two of them.
Step 3: Drag "Get Selected Finder Items" into your Workflow
Step 4: Drag "Rename Finder Items" into your Workflow. At this point it will ask you if you want to also add a "Copy Finder Items" action so that you're not changing the names of your only copy of these. Choose wisely.
The choice is yours
Step 5: Set your Rename options with the Dropdown. It starts on "Add Date & Time" but you have a lot of options, including one of my favorites: Replace Text.
Creating simple Automator workflows can make your life way easier
Then just go to the Finder, select the items you want to rename and, with them highlighted, come back into Automator and click the "Run" button in the upper-right hand corner. You can choose to save this workflow if you like, or you can just recreate it in the future if you like.