La bicicleta és ràpida.

• la = the feminine singular definite article, the
• bicicleta = bicycle / bike
• és = is (from the verb ser)
• ràpida = fast

So the structure is:

• La bicicleta = the subject
• és = the verb
• ràpida = an adjective describing the subject

This is a very normal Catalan sentence pattern: subject + verb + adjective.

Because bicicleta is a feminine noun in Catalan.

Catalan definite articles change for gender and number:

• el = masculine singular
• la = feminine singular
• els = masculine plural
• les = feminine plural

Since bicicleta is feminine singular, it takes la: la bicicleta.

Often, nouns ending in -a are feminine in Catalan, and bicicleta follows that common pattern.

But there is no rule that works 100% of the time, so the safest habit is to learn nouns together with their article:

• la bicicleta
• el cotxe
• la taula

That way, you learn both the word and its gender at the same time.

Because Catalan adjectives usually agree with the noun they describe in gender and number.

Since bicicleta is feminine singular, the adjective must also be feminine singular:

• masculine singular: ràpid
• feminine singular: ràpida
• masculine plural: ràpids
• feminine plural: ràpides

So:

• El cotxe és ràpid.
• La bicicleta és ràpida.

Even though ràpida comes after the verb, it still agrees with bicicleta.

És is the 3rd person singular present form of ser, meaning is.

Catalan often distinguishes between ser and estar:

• ser = used for identity, description, or more inherent characteristics
• estar = used more for states, conditions, or location in many cases

Here, fast is treated as a characteristic of the bicycle, so ser is the natural choice:

• La bicicleta és ràpida. = The bicycle is fast.

Using està here would usually sound unnatural.

The accents help with stress and, in some cases, distinguish words.

• és has an accent to distinguish it from es, which can be a pronoun
• ràpida has an accent to show that the stress falls on the first syllable: RÀ-pi-da

Accent marks are very important in Catalan, because they often tell you how a word is pronounced and sometimes which word it is.

A simple learner-friendly approximation is:

lah bee-see-KLEH-dah ez RAH-pee-dah

A few notes:

• bicicleta is stressed on -kle-
• és sounds like ez or ess, depending on dialect and context
• ràpida is stressed on the first syllable: RÀ-
• pronunciation varies across Catalan-speaking regions, so you may hear slightly different vowels

If you want a more careful version, you can think of it as:

la bi-si-KLE-ta és RÀ-pi-da

Yes, this sentence uses the most neutral word order:

subject + verb + adjective

• La bicicleta = subject
• és = verb
• ràpida = adjective

That is very similar to English: The bicycle is fast.

Catalan can change word order for emphasis or style, but La bicicleta és ràpida is the standard, straightforward version.

In normal Catalan, Bicicleta és ràpida is not a natural sentence.

You normally need the article here:

• La bicicleta és ràpida.

Catalan often uses definite articles in places where English may or may not use them. So for a regular sentence with a noun like this, keeping la is the correct choice.

If you remove the article, it sounds incomplete or unnatural in ordinary speech.