Let's have a short class.
De-ice is a system that sheds ice after accumulation.
Anti-ice is a system that prevents ice from forming in first place.
Pnuematic wing de-icers fall in this catagory, they don't function properaly untill a sufficient amount of ice has built up on the leading edges. If the de-ice boots are inflated too early the ice will have an elastic property that will prevent it from shedding.
Some aircraft utilize engine bleed air that directs hot air onto windscreens to melt ice away, this is also a de-ice system. Some aircraft have an isoprophol alcohol system that sprays this medium on the windscreen. Also a de-ice system, removing the ice after it has accumulated.
Some aircraft utilize anti-ice systems, this theoretically prevents ice from building up in the first place.
Electric windscreens for example, bleed air heated airfoil leading edges also.
In the case of engine inlets, never turn on engine inlet heat before engine igniters are actuated. Why, if ice builds up on the engine inlets and you turn on the anti-ice it will melt and get sucked into the engine. What happens when you throw a bucket of water on a camp fire, it goes out. That's a bad thing at 30,000 feet. If the ignitors are turned on first you have an ignition source to re-light that fire.