Eating fungi in Australia can be a dangerous practice as many of the Australian species have yet to be fully classified. The common Field Mushroom may be eaten without any problems, providing of course, it has been correctly identified in the first place. It should have the following features:

A white dome up to 10cm in diameter, with a ground stem.
The gills underneath the dome should NOT be white in colour but rather should be pinkish or slightly fawn. They should give off a distinct mushroom smell when crushed.

Field Mushrooms often appear after rainfall and prefer well watered . . .