As stated, most computers that do not come with a recovery disk have either a recovery partition or an utility on the machine to make recovery discs when you first get the machine. You'll need to purchase the discs from Toshiba, or from a third party.
http/www.recovery-disks.com carries recovery discs for many computers. I would suggest purchasing your disc set there:
http/www.recovery-disks.com/toshiba-satellite-a105-s4094.html
Is the link for your toshiba satellite a105-s4095 recovery disk set. It will come with the CD's and instructions. We install them all the time for customers and they are fairly easy, even for the lay person. If you have any trouble installing them, please contact the company, or come back here and ask us the question. We can usually point you in the correct direction. Also, we've ordered our discs from them for customers in the past and have not had any issues thus far.
Installation of the recovery discs is fairly straight forward once you get them. Of course, remember that the next time you buy a computer, make sure you make the CD's or you get them from the manufacturer with the computer.