The root verb is tener, to have
yo tengo, I have
tú tienes, you have
él tiene, he has
ellos tienen, they have
nosotros tenemos, we have.
- (Tú) tienes un gato [singular informal].
- (Vos) tenés un gato [singular informal in some places in America].
- (Usted) tiene un gato [singular formal].
- (Vosotros/vosotras) tenéis un gato [plural informal in Spain; not used in America].
- (Ustedes) tienen un gato [plural formal in Spain; plural general in America].
Ok, so in Spanish there are two ways of saying "you" (singular), used in different social contexts. You can either say "tú", or "usted". When using "tú", the correct conjugation of the verb "tener" (to have) is "tienes". Example: "tú tienes un gato" (you have a cat). When using "usted", the correct form is "tiene". Example: "usted tiene un gato"
Can someone explain me when and why I have to add '¡' '¿' in the sentence.
¡ is used at the beginning of an exclamation. ! is used at the end.
¿ is used at the beginning of a question. ? is used at the end.
They exist because the same words sequences can be used to make a statement or a question, so it makes it clear in writing what the intention is..
Having said that, Duo does not validate punctuation except for apostrophe and quotation marks, so using punctuation is generally optional.
Similarly, Duo only issues warnings about errors relating to accents, so it is up to you whether to use them.
My personal opinion is to get into the habit of using all the correct punctuation and accents from the beginning. At some point you may be writing for someone other than Duo!