Wrap up the soiled instruments to be autoclaved, seal the package with special striped tape. Put it into the autoclave and run it through the cycle. Open the door, observe that the stripes turned dark, and you can be confident that the instruments have been sterilized.
Autoclaves require specified temperature and pressure levels to be reached in order to sterilize.
The tape measures only that the temperature was hot enough. Your instruments may not be sterile. The only way to verify that your autoclave is working properly is to test it using known microorganisms. If the autoclave cycle kills them, it's working. If not, your patients may be at risk.