Scripts for beginners.

Hi everyone! I don't want to spoil anything, but I really need help with a script. I want to make it so that during the final battle, the boss casts a special spell – summoning angels. Angels should appear in the arena with accompanying effects of rays from Divine power. How can I do this?

Added 3 hours 9 minutes ago
And also – I've had problems with the StartCombat script for a long time . Can someone explain this script in detail? (preferably with examples)