how to restore macbook without CD

Mac's that came from the factory with OS X 10.7 or later have a hidden boot partition called Recovery HD, and also Internet Recovery which allow formatting and reinstalling of OS X from Apple's servers on a fast reliable Internet connection, a users AppleID and password.

A partition is a section on the drive that is another volume, can contain files or another operating system.

Recovery HD is basically a bare bones operating system that contains Disk Utility, Safari, Terminal, OS X reinstaller etc.

Older Mac's that were upgraded to 10.7 or 10.8 may not have Internet Recovery ability and thus have to resort to booting of the 10.6 disk to wipe the entire drive, however they do have Recovery HD partition which can erase and install 10.7 or 10.8 onto the Macintosh HD partition.

A wired or built in keyboard is probably required for any at boot keyboard commands. A PC one will work.

It's hold command r at boot time for Recovery HD, which can erase and/or reinstall the current OS X version

It's hold command option r at boot time for Internet Recovery, which can erase and/or reinstall the original OS X that came with the machine. (it won't install 10.7 over 10.8 and leave your 10.8 files and programs intact, for that the entire partition needs to be erased first)

Anytime you reformat or erase a partition or the entire drive, all the data on that partition or the drive being targeted is lost permanently and only in some cases recoverable with expensive time and software.

If you have a Mac that originally came with 10.4, 10.5, or 10.6-10.6.2 from the factory, then you can use the 10.6.3 white Snow Leopard retail disks Apple sells online (sans iLife, but can be reinstalled via the 10.5 disks or using Pacifist from CharlesSoft)

If you have a Mac that originally came with 10.6.3 or later, then you have to order machine specific 10.6 disks from Apple.

You can't order 10.4 or 10.5 disks, Apple doesn't support those OS X versions anymore for anything, even security updates, but they can be found on eBay etc.

If you dont' know what operating system originally came with your machine, you can install MacTracker and use the Apple Menu > About this Mac > More information to look for the model, like "MacBook Pro 4,1" and search for it there. If your Mac is not booting, you can find the serial number of your Mac and enter it into a online database that will tell you the model of the Mac.

To boot from a disk, hold the c or option/alt keys while booting the computer, choose the disk and click the arrow.

If you want to erase and install OS X fresh, with no files or programs, like to sell the machine without your personal data, then you head to Disk Utility (on the 10.6 disks or via Recovery) FIRST, then erase, then quit and install OS X.

If your wanting to erase or format the ENTIRE drive (like a new one), this includes deleting the hidden GUID, EFI and all partitions on the drive (including BootCamp and Macintosh HD) for malware problems (like from Windows 8+ malware in EFI partition or a Linux install attempt) it can be done via the 10.6 disk, or via Internet Recovery only, not via Recovery HD.

OS X 10.6-10.8 have the ability to overwrite their same OS X version with a new copy, keeping files and programs intact, this is to fix issues with OS X and third party kext files in OS X.

Installing OS X over itself in doing so it boots out third party at boot kernel extension files installed in OS X, so make sure first you can reinstall those software's that do this. Keeping the original installer package when originally installing them is a ideal method to thwart this. This advice is mainly now for 10.6 users who some developers are prematurely dropping for only offering their software for later 10.7 and 10.8 users to force a upgrade purchase, but if contacted, likely can provide 10.6 version installers of their software via email. The third party at boot kext files can be located in the System/Library/Extensions folder if you know their names, and can remove them prior to the OS X being reinstalled over itself, then placed back into that same folder later. If OS X is not booting this can be done by creating a external OS X boot drive and accessing the internal drive folders and also retrieving personal files.