Forum:About using Field Spell Card(s)

Can I use field spell card if my spell/trap card zone is full? What I mean is when I activate field spell card, do I have to place it on the spell/trap card zone and then it is sent to field card zone when it resolves, or I only have to place it directly on my field card zone? The Game Mechanic thread says that

 If a Field Spell Card is active, and a new Field Spell Card is activated, and if activation of that card is chained to with a card that destroys it, like Mystical Space Typhoon or Dust Tornado, the already-active Field Spell Card will remain on the field.

Could anyone please explain the meaning of the above sentence for me(my English is bad), by the way, can I use something like stardust to chain to my opponent's activation of field card, if I(or him) already control one?