Estiro el braç.

Estiro is the first-person singular present indicative form of estirar.

So:

• estiro = I stretch
• depending on context, it can also correspond to English I am stretching

The ending -o tells you the subject is I.

Yes. Estirar is a regular -ar verb.

Its present-tense forms are:

• estiro
• estires
• estira
• estirem
• estireu
• estiren

So estiro follows a normal conjugation pattern.

Catalan often leaves out subject pronouns because the verb ending already shows who the subject is.

So Estiro el braç is the normal way to say it.

You can say Jo estiro el braç, but that usually adds emphasis or contrast, like:

• Jo estiro el braç, no la cama.

With body parts, Catalan very often uses the definite article instead of a possessive when the owner is clear from context.

So el braç can naturally mean my arm here.

You can still say el meu braç if you want to be especially explicit or contrastive, but it is often unnecessary.

Yes. In standard Catalan, a singular countable noun normally needs a determiner.

So:

• Estiro el braç = correct
• Estiro braç = not standard

If you do not use el, you would normally need some other determiner, such as:

• un braç
• el meu braç
• aquest braç

It can mean either one, depending on context.

Estiro el braç can mean:

• I stretch my arm as a general or repeated action
• I am stretching my arm right now

If you want to make the ongoing action more explicit, Catalan can also use:

• Estic estirant el braç

Braç is pronounced roughly like bras.

The letter ç is called ce trencada, and it represents an s sound.

So:

• braç sounds like bras
• the final ç is not silent

A simple approximation is es-TEE-ro.

A few helpful points:

• the stress falls on ti
• the r in estiro is a single tapped r, not the strong rolled rr
• in many accents, the first vowel may sound quite light

Yes, braç is masculine singular, which is why it takes el:

• el braç

The plural is:

• els braços

So:

• el braç = the arm
• els braços = the arms

This is the normal, neutral word order: verb + object, with the subject omitted.

Other orders are possible, but they usually add emphasis or sound more marked:

• Jo estiro el braç = emphasizes I
• El braç l’estiro jo = strong contrast or focus

For a learner, Estiro el braç is the best standard pattern to remember.