"Please, I need to use the car."
Translation:Por favor, yo necesito usar el carro.
Because "necesitar" was already conjugated (changed to "necesito"), and you only personalize the first verb in a series.
This is the same reason we don't say in English "She wants goes to the movies." and instead leave "to go" in the impersonal infinitive form (She wants to go to the movies.).
Both words are used more or less depending on the region.
I learned Spanish at school in England over 30 years ago & am refreshing (almost starting again) with this course. There are a couple of words that are different to what I learned before. Car was el coche not el carro, a ticket I think was un bilete not un boleto. Are the words I was taught old fashioned? Are there different nuances to these words or is there a difference between the words used in Spain & words used in other Spanish speaking parts of the world? Thanks..
You can basically always leave it out.
Duolingo tends to include subject pronouns because they're trying to introduce the grammatical concepts (i.e. so you can see how "yo" corresponds to "I" in English). You don't see these pronouns used much in natural Spanish writing, but it's not wrong to include them.
To my knowledge, tener is a possesive verb, and would make the sentence similar to "I have the use of the car" (which makes very little sense) and instead of "I need to use the car. "Need" and "have" are used interchangeably in English, however, are not interchangeable in Spanish
When using tener to describe a feeling, it maintains this possesive form, as in "Yo tengo hambre" which directly translates to "I have hunger". This does not make sense in English however, and is thus translated to "I am hungry"
No, there is no reason. The complete sentence is with the subject 'Yo necesito', but it is not common spoken language, maybe unless you really stress the subject. You can say "No voy a hacerlo" in general. But if you want the stress that not you but someone else will do it, you probably say "Yo no voy a hacerlo, pero tú sí".