Why is there a "це"?
"Це" is often used in "A is a B"-type sentences that are "definitions" classifying some things through other things (Кіт — це тварина). It is optional, though.
Київ — столиця and Київ — це столиця are equivalent.
Київ - це столиця. is like "Kyiv - it's a capital"
Because we tend to omit є, це is quite a handy thing to use to make clear that what you're saying is a "definition"