Find an ideal location to install the rain catcher cup. Good locations are a deck railing, fence post, mailbox post or in the middle of the yard on a dedicated mount. The location should be well away from any object that is taller than the gauge, like a roof or tree. This will block the rainfall from making it into the gauge affecting your measurements.
Hold the rain gauge's mounting bracket to the post and make sure it is perfectly straight by holding a level against the side of it.
Install two screws through the mounting brackets holes with a screwdriver. Tighten snugly, but do not over-tighten, as this may damage the plastic mount.
Insert the rain catcher cup into the mounting bracket and wait for the next rainfall.