Language / Jest/To jest - to jest is often abbreviated to just to [24]

It's obvious that to jest is often abbreviated to just to. (e.g. To świetna piosenka!)

But in a sentence like:
"X is Y" (where X is a noun and Y is an adjective)
the word "is" is sometimes translated into just jest and sometimes into to jest (often abbreviated to just to).

Examples of the 2 constructions:
1. Samochód jest biały.
2. Kolokwium to (jest) dużo pracy.

So when are you supposed to use just jest, and when to use to (=to jest)? In a sentence that begins with a noun. Of course "to" can be a substitute for the noun, but that's not the kind of sentences that I mean now.

Thanks in advance!