Vanha kodinkone käyttää paljon sähköä.

That is a very common point of confusion.

The verb käyttää has:

• the dictionary form / infinitive: käyttää = to use
• the 3rd person singular present tense: käyttää = uses

So in isolation, käyttää can mean either to use or uses.
In this sentence, it must mean uses, because it comes after the singular subject vanha kodinkone.

So:

• vanha kodinkone käyttää = an old appliance uses

Context tells you which meaning is intended.

Because Finnish uses the partitive case here: sähköä.

There are two main reasons for that in this sentence:

• paljon normally requires the following noun to be in the partitive
  
  • paljon sähköä = a lot of electricity
• with substances or uncountable things like electricity, Finnish often uses the partitive when talking about some amount rather than a whole, countable item

So:

• sähkö = electricity, electric power
• sähköä = electricity in the partitive, roughly some electricity / electricity as an amount

That is why paljon sähköä is the natural phrase.

Paljon means a lot, much, or a lot of.

In this sentence it tells you the amount of electricity being used:

• käyttää paljon sähköä = uses a lot of electricity

A useful pattern to remember is:

• paljon + partitive noun

For example:

• paljon vettä = a lot of water
• paljon aikaa = a lot of time
• paljon rahaa = a lot of money

So paljon sähköä follows a very common Finnish pattern.

Yes. Vanha agrees with kodinkone.

Here both are in the nominative singular:

• vanha = old
• kodinkone = household appliance / home appliance

So:

• vanha kodinkone = an old appliance

In Finnish, adjectives usually match the noun in number and case.

Compare:

• vanha kodinkone = old appliance
• vanhan kodinkoneen = of the old appliance
• vanhat kodinkoneet = old appliances

So the form vanha is exactly what you expect here.

Kodinkone is a compound noun.

It is made from:

• koti = home
• kodin = of the home
• kone = machine

So kodinkone literally means something like home’s machine, which is why it means household appliance or domestic appliance.

Finnish uses compound words very often, so this is a useful example of how meaning gets built up from smaller parts.

Because Finnish does not have articles like English a, an, and the.

So:

• vanha kodinkone can mean an old appliance or the old appliance

The exact meaning depends on context.

In a standalone example sentence, English often chooses an old appliance because it sounds more natural unless a specific appliance has already been mentioned.

This is the normal basic word order in Finnish:

• subject + verb + object

So:

• Vanha kodinkone = subject
• käyttää = verb
• paljon sähköä = object/amount expression

That makes the sentence very straightforward.

Finnish word order can change for emphasis, but this version is the neutral, standard one.

Yes. It is the object, but it is a partitive object.

Finnish objects are not always in one single form. They can appear in different cases depending on meaning. One very common option is the partitive, especially when:

• the thing is an uncountable substance
• only an unspecified amount is involved
• the action is seen as ongoing or not reaching a complete result

Electricity is not a countable item like one chair or two books, so sähköä in the partitive is natural here.

So you can think of:

• käyttää sähköä = use electricity
• käyttää paljon sähköä = use a lot of electricity

You would make the subject plural, and the verb would also change to plural:

• Vanhat kodinkoneet käyttävät paljon sähköä.

Breakdown:

• vanhat = old, plural
• kodinkoneet = appliances
• käyttävät = use
• paljon sähköä = a lot of electricity

So Finnish changes both:

• the adjective
• the noun
• the verb

to match the plural subject.

In normal usage, kodinkone usually means a household appliance, especially larger electrical ones.

Typical examples are:

• washing machine
• dishwasher
• refrigerator
• oven

So in this sentence, kodinkone strongly suggests an appliance that consumes electricity, which fits naturally with käyttää paljon sähköä.

A few key points help:

• Finnish stress is normally on the first syllable
• double vowels are pronounced longer
• ä is a front vowel, somewhat like the vowel in British cat for many learners, though not exactly the same

So käyttää has:

• stress on käy-
• a long final -ää

Also, every written sound is usually pronounced clearly, so Finnish spelling is quite consistent.

A rough learner-friendly approximation might be:

• KÄYT-tää

But it is best to listen to native audio if possible, especially for ä and vowel length.

Yes, and in many contexts that is even more natural.

Both verbs can work, but there is a nuance:

• käyttää = uses
• kuluttaa = consumes

With electricity, Finnish often uses kuluttaa when talking about energy consumption:

• Vanha kodinkone kuluttaa paljon sähköä. = An old appliance consumes a lot of electricity.

Your original sentence with käyttää is still understandable and correct, but kuluttaa sähköä is a very common collocation when discussing energy use.