I think VX is the same as XP here. (I really need to get VX)
"Through" is typically used for events that are 'laying on the ground'. i.e. the player can pass right through them.
If you set a moving NPC event to "through", it will walk through other events, and the player.
Triggers are listed & explained in the help docs. (I highly recommend reading it. All of it. At least the first section, "RPG Maker VX". the second section, "RGSS Reference" is for scripting.)
Action Button
The event runs when the player presses the action button (C) when in contact with the event. The event also runs even if there's a counter tile between the player and the event. Use this trigger for basic actions such as speaking with villagers and examining treasure chests.
Player Touch
The event runs under the same conditions as the [Action Button] trigger, as well as when the player uses the directional buttons to come in contact with the event. The event will run when the player and event overlap as well, provided that is permitted. Use this trigger for movement events.
Event Touch
The event runs under the same conditions as the [Player Touch] trigger, as well as when the event comes in contact with the player. Use this to trigger a battle when a monster touches the player wandering around the map.
