Well, not necessarily. CCleaner is a hard drive cleaning utility, which basically means it gets rid of unnecessary files on your computer. Now, it can be kind of aggressive, which is why you should read up on how to use it and be very careful when adjusting the settings of the program. I'll try to give you a good idea of what to do here, though please feel free to research it on other sites as well.
CCleaner is brought to you by the company Piriform, and can be downloaded here. (Yes, there's a free and paid-for version. If you hit the "Download" button you'll get the free version, which I use and am perfectly happy with.)
The most recent version (as of writing) was released on July 25, 2013. My version is a little dated, so the screenshots I take might look a bit different from the version you have on your system. After you download and install CCleaner, create a desktop shortcut, and open the program, you should get a window that looks somewhat like this:
Look all the way to the left. You see the tabs "Cleaner", "Registry", "Tools", and "Options". "Cleaner" is the one CCleaner automatically opens up in, and it's the most important one.
In the middle, you see two tabs of checklists. These are the settings for what you want to clean off your computer. It's very important that you determine these settings carefully, since you're deciding what's going to be PERMANENTLY deleted from your computer.
(While we're on the subject: I assume no liability for any damage that is done as a result of using this program incorrectly or carelessly. In addition, what you see in these checklists are my own personal settings that ONLY I USE. They are not intended to serve as guidelines for what you should do. Only you can make that decision.)
The "Windows" tab is, obviously, for Windows applications and applies to Windows users only. "Internet Explorer" is all about temporary Internet files and cookies. "Windows Explorer" deals with stuff like recently opened files and recent searches (and, if you use the "Run" bar, the files that store the names of the most recent programs you've run). Under "System", you have files relating to your clipboard (which stores the stuff you "copy and paste"), the Recycle Bin, and temporary files that help certain programs open faster.
Now, I want you to take a close look at this.
Look under "Advanced". All sorts of bizarre things to make beginners' heads spin. I strongly recommend that you do NOT mess with this section until you've familiarized yourself with everything in that checklist. In fact, some choices in this section will give you a warning message if you select them. It's not that it's stuff only fit for IT geniuses of the highest training; it's just a bit more complicated and it would be easy for someone who is new to CCleaner to delete something that they don't want deleted.
There's another tab, too—"Applications". It's basically more of the same, more checklists asking you what you want to get rid of. Just be careful when making your decisions.
Once you have the settings to your liking, hit "Analyze". This may take a while, depending on how much "junk data" you have on you computer.
You can review what is set to be deleted one last time. Double-clicking anything in this list will give you another list of every single file that is marked for deletion. If you don't want a file deleted, right-click and select "Add to Exclude List".
Once you're happy with your "delete list", hit "Run Cleaner". CCleaner will ask you if you're sure, and if you click "Yes", it'll begin cleaning. Again, if you have a lot of unnecessary files, it might take a few minutes.
That's the main part of the cleaner. There's also a Registry cleaner, which runs in a very similar way. I would be more careful with the Registry cleaner because Registry keys are more likely to be critical to your system. In other words, you're more likely to accidentally delete something important here than you are with the regular cleaner. However, getting rid of certain keys can also help your computer to run more efficiently, so I'll cover it anyway.
First off, hit the "Registry" tab, and you'll get something that looks like this.
Notice how I have everything checked. You probably don't understand what most—if any—of this is, and that's okay. If you would feel better doing your research before messing with this part of the Cleaner, or not using it at all, then that's totally fine. However, if you're feeling gutsy, go ahead and check what you want in the list and hit "Scan for Issues".
If there are no out-of-place registry keys, it'll say "No issues were found". (That's what happened with me just now, and it's why you won't be getting any more screenshots.) If it finds some keys worth cleaning out, it will list them. Once again, you can choose to delete certain keys and add others to the "Exclude" list.
Once you have your list of keys to delete, hit "Fix Selected Issues". You will be asked if you want to back up changes to the Registry. Answer "yes". Save the file, and then proceed with the cleaning. You can fix each issue individually or fix them all at once; the options are pretty intuitive here.
After cleaning out the Registry, wait after you use your computer a few times to make sure everything's working properly, and then you can delete your backup file. Be sure that you know where the file was placed when you saved it. (Mine always saves in Documents.)
And that's really it for the basics of CCleaner. Obviously, there's much, much more to the program. However, this is what you need to know to keep your computer clean. I like to run CCleaner once or twice a week; you decide what's best for you. And, as always, the most important thing you can do is be careful, giving strong consideration to any settings you put in place. If you do that, then using CCleaner should be no problem.