Ask to be trained in cleaning medical instruments during your job orientation. If it's your responsibility to clean medical instruments, then the person responsible for your on-the-job training should show you how the machines work, in addition to explaining hospital policy on cleaning instruments.
Read the instruction manual for the machine you're using. Medical instruments are usually cleaned through steam heat, ultrasound or chemical baths. For cleaning large numbers of medical instruments, hospitals usually purchase specialized machines.
Gather information from your more experienced coworkers. If it is your responsibility to clean medical instruments, then your coworkers should be able to show you what to do. Once the process is explained and you've walked through it, you can use your manual as a guide to do it on your own.