There are a number of ways to identify an orchid you have found; some of these almost certainly subject to a bit of educated guesswork while others are potentially more reliable. You can ask an expert what they think the orchid is or you can try and match the orchid to a description and illustration in a book. You can also go online and post a photo into one of the many specialist forums asking if anyone can identify it and finally, if one is available, you can use a key. There are several types of keys including electronic keys such as Lucid, and WANOSCG is in the early stages of developing one of these. However, the oldest and most commonly used type of key is the dichotomous key.
A dichotomous key is an identification tool that consists of a series of paired statements or clues about features or characteristics of the orchid, providing a step-wise guide toward identifying it. As you proceed from one step to the next, the clues gradually narrow down the list of possible orchids until you are left with just one. In order to use a dichotomous key you will need to be able to view a whole plant including the flower and leaf as both may be required to successfully identify the orchid. You may also need other information such as location, flowering time and habitat.
There are 28 genera of orchids in the south-west of Western Australia with dichotomous keys currently available for just five of these. These five keys can be found here along with two subspecies keys. Note: some of these keys are also available online at https://keybase.rbg.vic.gov.au/projects/show/7