Quando piove, accendo i tergicristalli e tengo le mani ferme sul volante.

In Italian, weather verbs are usually used without an expressed subject.

• Piove = it rains / it is raining
• Italian does not normally say esso piove

This is similar to English in meaning, but different in structure. English needs it, while Italian does not.

Other examples:

• Nevica = it is snowing
• Fa caldo = it is hot
• Fa freddo = it is cold

Italian often uses the present tense to talk about:

• habits
• general truths
• things that usually happen

So Quando piove means:

• When it rains
• Whenever it rains

It does not have to mean only what is happening right now. In this sentence, it sounds like a habitual action: whenever it rains, I turn on the windshield wipers and keep my hands steady on the steering wheel.

The comma separates the introductory time clause from the main clause.

• Quando piove = subordinate clause
• accendo i tergicristalli e tengo le mani ferme sul volante = main clause

This is very natural in Italian, especially when the quando clause comes first.

You may also see similar punctuation in sentences like:

• Quando arrivo, ti chiamo.
• Se piove, resto a casa.

Accendo is from accendere, meaning:

• to turn on
• to switch on
• to light

So accendo i tergicristalli literally means I turn on the windshield wipers.

Italian often focuses on the idea of switching something on, not just using it.

A few examples:

• Accendo la luce = I turn on the light
• Accendo la radio = I turn on the radio
• Accendo i tergicristalli = I turn on the windshield wipers

Because windshield wipers normally come as a pair, Italian usually refers to them in the plural:

• il tergicristallo = one windshield wiper
• i tergicristalli = windshield wipers

The article i is the masculine plural form of the.

So:

• accendo i tergicristalli = I turn on the windshield wipers

Tergicristalli is a compound noun.

It comes from:

• tergere = to wipe
• cristalli = glass panes / windows

So the word literally suggests something like glass-wiper.

Even though the second part looks plural, the whole word functions as a normal noun:

• singular: il tergicristallo
• plural: i tergicristalli

This kind of compound word is common in Italian.

Fermo / ferma / fermi / ferme means still, steady, motionless.

So:

• Tengo le mani sul volante = I keep my hands on the steering wheel
• Tengo le mani ferme sul volante = I keep my hands steady on the steering wheel

The adjective adds the idea that the hands are stable and not moving around.

This is a very natural structure in Italian:

• tenere + noun + adjective

For example:

• Tengo la porta aperta. = I keep the door open.
• Tengo gli occhi chiusi. = I keep my eyes closed.
• Tengo le mani ferme. = I keep my hands still.

Because ferme agrees with le mani.

• mano is a feminine noun
• plural: mani
• with article: le mani

Since the noun is feminine plural, the adjective must also be feminine plural:

• masculine singular: fermo
• feminine singular: ferma
• masculine plural: fermi
• feminine plural: ferme

So:

• le mani ferme = the still/steady hands

A useful reminder: even though mano ends in -o, it is feminine:

• la mano
• le mani

Italian often uses the definite article instead of a possessive with body parts, especially when the owner is already clear.

So Italian prefers:

• tengo le mani ferme

rather than:

• tengo le mie mani ferme

Both are understandable, but le mani sounds much more natural here because it is obvious whose hands they are: the speaker's.

This is very common in Italian:

• Mi lavo le mani. = I wash my hands.
• Chiudo gli occhi. = I close my eyes.
• Alzo la testa. = I raise my head.

Sul is a contraction of:

• su = on
• il = the

So:

• su + il = sul

And volante means steering wheel.

Therefore:

• sul volante = on the steering wheel

Other similar contractions:

• su + lo = sullo
• su + la = sulla
• su + i = sui
• su + gli = sugli
• su + le = sulle

Examples:

• sul tavolo = on the table
• sulla sedia = on the chair

Because volante has several meanings depending on context.

Common meanings include:

• steering wheel
• flying / mobile as an adjective in some contexts
• flyer / leaflet

In a driving sentence, volante clearly means steering wheel.

For example:

• Tengo le mani sul volante. = I keep my hands on the steering wheel.

Context usually makes the meaning obvious.

Italian usually leaves out subject pronouns when the verb ending already shows the subject.

• accendo = I turn on
• tengo = I keep

The -o ending tells you the subject is io.

So Italian normally says:

• Quando piove, accendo i tergicristalli e tengo le mani ferme sul volante.

rather than:

• Quando piove, io accendo i tergicristalli e io tengo le mani ferme sul volante.

The pronoun io is only added for emphasis, contrast, or clarity.

Grammatically, the Italian present tense can sometimes correspond to:

• simple present
• present progressive

But in this sentence, the most natural reading is habitual:

• When it rains, I turn on the windshield wipers and keep my hands steady on the steering wheel.

If you wanted to strongly emphasize an action happening right now, Italian would often use:

• sto accendendo
• sto tenendo

But here the plain present works best because it describes what one normally does while driving in the rain.