Learn Italian: C'è molto traffico oggi? - Is there a lot of traffic today?

It is a combination of ci (there) and è (is). Because è starts with a vowel, Italians drop the i in ci and use an apostrophe to make it flow better. Together, it means "there is".

How do you tell the difference between "There is a lot of traffic" and "Is there a lot of traffic?"

In Italian, you don't change the word order to make a question like we do in English. You use the exact same words: C'è molto traffico oggi. In writing, the question mark tells you it's a question. When speaking, you simply raise the pitch of your voice at the end of the sentence.

Could I use ci sono instead of c'è in this sentence?

No, because traffico (traffic) is treated as a singular noun. You use c'è (there is) before singular things, and ci sono (there are) before plural things.

Why does this sentence use molto instead of molti?

Molto means "a lot of" or "much", and its ending has to match the word it describes. Because traffico is a masculine singular noun, molto stays in its masculine singular form. If you were talking about "many problems" (problemi, which is plural), you would use molti.