Yes, it can be used in cider. It should not effect flavor. I would use it after fermentation has stopped, and when you rack into a secondary for clearing. Then, it's just a matter of following the directions. Below are the directions I have on the bottle I got from my LHBS, yours may vary.
DIRECTIONS: Dissolve 1 TBSP Sparkolloid in 1 Cup (8 fl oz) of boiling water for 5 minutes. Add mixture to 6 Gallons (23 Liters) of wine (or cider). Stir gently. Wait one week (I go two weeks) before bottling.