Learn French: C'est une décision importante. - It is an important decision.

In French, when you say "it is" followed by a noun phrase (a noun with an article like une), you use c'est. You would only use elle est if an adjective followed immediately after, like in Elle est importante (It is important).

Why does the adjective importante come after décision?

Most adjectives in French are placed after the noun they describe. Only a specific group of short, common adjectives (usually dealing with Beauty, Age, Goodness, or Size) go before the noun. Since importante doesn't fall into those exceptions, it goes after.

Why is there an "e" at the end of importante?

Adjectives must match the gender of the noun they describe. Because décision is a feminine noun (which we can see from the feminine article une), we add an e to the masculine word important to make it feminine.

How does the feminine spelling of importante change its pronunciation?

Adding that feminine e at the end forces you to pronounce the "t" right before it. In the masculine form important, the final "t" is completely silent, but in importante, you clearly hear a "t" sound at the end.