The outdoor unit of a heat pump is the part you can inspect from the yard. The installer does most of the work on it, and you can follow along. Here is the order the work usually takes, and what you are looking for at each step.
Confirm the spot before anything is poured. The unit needs clear space on all sides for airflow. Check the clearances in the manufacturer's manual against the wall, the fence, and any shrubs. Look up as well. The unit should not sit under a drip line, and it should not sit where the exhaust air blows into a window. Confirm the spot with the installer before the pad is made.
Set the pad level and above grade. The pad holds the unit off the ground so water runs away from the base. A level pad keeps the unit from resting on one corner. Ask what the pad is made of and how it is anchored. Ask that it be checked for level before the unit is set on it.
Route the line set with support. The line set is the pair of refrigerant lines that run between the outdoor unit and the indoor coil. Refrigerant connections and charging are hired work for a licensed installer. Your part is to see that the lines are supported, protected from sun and foot traffic, and sealed where they pass through the wall. Ask the installer to show you the route before the wall is closed.
Set the electrical disconnect and confirm the power. A disconnect near the unit lets service staff shut it off safely. Local code sets where it goes and what it must be. Ask the installer to name the permit and inspection steps that apply where you live, and ask who pulls the permit. Electrical connections are hired work, so leave them to the licensed trade.
Set the condensate drain. The unit sheds water during cooling and during defrost. The drain should carry that water away from the foundation and should not pool at the base. Look at the drain outlet during the first run.
Run the test and keep the record. A proper startup includes runs in heating and in cooling, with the installer taking the readings the manufacturer calls for. Ask for those readings in writing and keep them with the manuals. That record is what you will compare against at the next service visit.
For the planning side of the same unit, read the Heat Pump page and set your planning date from the install day on the paperwork.