Translation:Are you tall?
That's correct. If you ever have a question about adjectives, you can look for them in https://dle.rae.es/alto?m=form so you can see if they have other forms. In the entry for "alto" you have "alto, ta" meaning that "alto" and "alta" have the same definition. Superscripts are used if there are more than one definition for the word ("alto" also means "stop" and "alta" means something like "entry").
A friend gave me a tip that greatly helped me with listening. (I stand to be corrected, please). Let me get this right. When a word ends with a consonant other than 'h' and the next word begins with vowel they sometimes mesh the pronunciation of the words together. When the word ends with a vowel and the next word also begins with a vowel the word is separated. So if - = vowel and + = consonant, the pronunciation looks something like the following: -&+/+&- = pronounce together. -&-/+&+ = pronounce separate. Because 'h' is not pronounced in Spanish if a word begins or ends in 'h' you would use the letter before or after depending if it's vowel or consonant. You think about English speakers who talk really fast, it's similar.
You can ask "¿Es alto?" as well, but since "es" isn't used just for "usted" (you could be asking for "his height" or "its height") it can be confusing; asking "¿es usted alto?" could be a little long; finally since you don't usually ask for height formally, you ask "¿eres alto?" most of the time.
The Spanish we're learning from Duolingo has two types of "You": the formal and the informal (or casual). The formal is "Usted", and the informal is "Tú", so both "usted" and "tú" means "you" (singular).
In English we say "You are…". This "are" has to agree with either "Usted" or "Tú", so they also have the corresponding types of this "
es…" and "Tú
eres…". In other words, you only use "eres" when you use the "Tú" version of "You".