To use the trainer correctly, as of V1, you can code in Lua in the text box at the bottom, then use the Execute button to execute it.
The global variable "Terraria" is where all of the custom stuff is. For example, "Terraria.Player" is where everything to do with the Player is stored.
Keep in mind, not EVERYTHING will be there. Only some things will be there that would actually make sense to modify, such as Health (CS) and Mana (which is CS anyway, so modifying that works)
(There will be more things added to this page soon)