Si una tecla no funciona, uso el ratón.

Si means if here, so it introduces the condition:

• Si una tecla no funciona = If a key doesn’t work

Be careful not to confuse si with sí:

• si = if
• sí = yes

The accent changes the meaning.

Because tecla is a feminine noun in Spanish.

So you use the feminine singular article una:

• una tecla = a key

A few related forms:

• la tecla = the key
• unas teclas = some keys
• las teclas = the keys

In this sentence, tecla means a key on a keyboard.

So una tecla no funciona means a key isn’t working or one key doesn’t work.

Spanish tecla can also refer more generally to a button or key, depending on context, but with ratón in the same sentence, a keyboard key is the natural meaning.

Spanish normally uses funcionar for machines, devices, buttons, keys, programs, etc. that work / function.

So:

• la tecla funciona = the key works
• la tecla no funciona = the key doesn’t work

Using trabajar would usually mean to work in the sense of a person working at a job, so it would sound wrong here.

Because the subject is una tecla, which is singular.

The verb funcionar changes to match the subject:

• yo funciono
• tú funcionas
• él / ella / una tecla funciona

So una tecla no funciona literally means a key does not function.

In Spanish, subject pronouns are often omitted because the verb ending already shows who the subject is.

• uso already means I use
• so yo is not necessary

That’s why uso el ratón naturally means I use the mouse.

You could say yo uso el ratón, but that would usually add emphasis, contrast, or clarity.

Spanish often uses the present tense for general truths, habits, and repeated situations.

So:

• Si una tecla no funciona, uso el ratón.

means something like:

• If a key doesn’t work, I use the mouse
• Whenever a key doesn’t work, I use the mouse

This is a normal way to express a real or habitual condition in Spanish.

The comma separates the if-clause from the main clause:

• Si una tecla no funciona, = condition
• uso el ratón. = result

In Spanish, it is very common to put a comma when the si clause comes first.

If the order were reversed, the comma would usually disappear:

• Uso el ratón si una tecla no funciona.

Both are correct.

Here el ratón means the mouse, referring to the computer mouse as a known, specific object in the situation.

Using el is natural because the speaker means the mouse they use, not just any random mouse.

Compare:

• uso el ratón = I use the mouse
• uso un ratón = I use a mouse / one mouse
  This sounds more like you are introducing it as just one example or one unspecified device.

Yes. Ratón literally means the animal mouse, and it is also the standard word for a computer mouse in Spain.

So:

• un ratón = a mouse / a computer mouse
• el ratón = the mouse

Context tells you which meaning is intended. In this sentence, because of tecla, it clearly means the computer device.

The accent mark shows where the stress goes: ra-TÓN.

Without the accent, Spanish pronunciation rules would suggest a different stress pattern, so the written accent is necessary.

This is just part of the correct spelling of the word:

• ratón = correct
• raton = incorrect

In Spain Spanish, ratón is the normal standard word for a computer mouse.

Many Spanish speakers would understand mouse, especially in tech contexts, but for standard Spanish—especially for Spain—ratón is the best choice.

So for a learner, uso el ratón is exactly the form you should know.

It usually means any key in a general situation.

Even though una tecla literally means a key, in this kind of sentence it often has a general meaning:

• Si una tecla no funciona... = If a key doesn’t work... / If any key isn’t working...

So the speaker is not necessarily talking about one particular key on one particular keyboard; it can describe a general habit or rule.