In the landscape lighting world, most of all the systems being installed are a 12 volt system which require a transformer. In this video, Scott Romacker goes over the key elements of a transformer and what you need to know.
Secondary fuse protects the transformer wires and light fixtures that are connected to the transformer.
This needs to always stay plugged in unless you are going to use a photocell. Without this loop installed or a photocell installed the transformer will not work.
This can be used to plug an internal timer or module to control the transformer. The electrical pigtail must be plugged into the transformer or the transformer will not work.