Learn Spanish (Latin America): Las flores rojas son bonitas.

The singular noun flor (flower) is feminine, even though it doesn't end in the typical -a. Because it is feminine and plural here, any adjectives describing it must also be feminine and plural. That is why we use rojas and bonitas, along with the feminine plural article las.

Why is it flores rojas instead of rojas flores?

In English, we put the descriptive adjective before the noun. In Spanish, descriptive adjectives like colors almost always come after the noun they describe. So, the red flowers becomes flores rojas (literally: flowers red).

Why does bonitas have an -s at the end if it comes after the verb?

In Spanish, adjectives must always match the noun they describe in both gender (masculine or feminine) and number (singular or plural), no matter where they are in the sentence. Since flores is plural and feminine, bonita becomes bonitas, even when it comes after the verb son.

Why use son instead of están for the word are?