Learn Turkish: Birinci güllü buket çok güzel. - The first bouquet with roses is very beautiful.

It is formed by adding the suffix -lü to the noun gül (rose). This suffix, which changes according to four-way vowel harmony (-lı, -li, -lu, -lü), turns a noun into an adjective meaning 'containing' or 'characterized by'. Because gül has the front rounded vowel 'ü', it takes -lü.

If it means 'with roses' (plural), why don't we use the plural suffix and say güllerli?

In Turkish, the -li suffix almost always attaches to the singular form of a noun, even when the English translation uses a plural. The suffix naturally implies 'containing the item', so güllü is the standard way to say it. Adding the plural suffix before it (güllerli) sounds very unnatural.

Why is the word order Birinci güllü buket instead of Güllü birinci buket?

In Turkish, determiners and numbers (like the ordinal number birinci, meaning 'first') generally come before descriptive adjectives (like güllü). This directly mirrors the English order: 'the first rose-filled bouquet'.

Where is the verb for 'is' in this sentence?

There isn't one! In Turkish present-tense statements about a third-person subject ('it'), the 'to be' verb is usually omitted. The adjective güzel at the end of the sentence stands alone to mean 'is beautiful'.