Here i'll explain the 2 basic ways to start your macro
/cast and /use both of them can be used for spells (melee ability's also count as spells, Sinister Strike for example), mounts, trinket, parachute cloak or even items from your inventory.
There is just one little difference between them.
/cast will use your equipped trinket, but if it's not equipped it will do nothing.
Where as /use will equip...