Wow! You really need to educate yourself bud!
You can find out what version of OSX it is running by clicking on the black Apple menu in the top left hand corner and then, 'about this Mac'.
You can also find the model number underneath the machine. Type the number into the search box of your browser and find out what you have.
As for removing your data: If it is a new machine you should reinstall the OS from the flash drive that came with it. That contains the version of OSX and iLife that it was released with. Other software should be removed so you are not breeching any licence agreements. Just insert the flash drive, go to system preferences, select the flash drive as start up disc and restart the computer. After it restarts, select the language and in the next window go to the file menu at the top and open the disc utility. Use it to erase the hard drive. Then, start the installer. After the installer has run turn the computer off by holding down the start button. Sell it to your brother and let him input his personal data.