Esperanto grammar

Esperanto's grammar (rules of language) is meant to be simple. The rules in Esperanto never change and can always be applied in the same way.
Articles.
Esperanto has only definite article "la" (the same thing as "the" in English) and no indefinite article (the same thing as "a" or "an" in English). They use definite article when they talk about things, about which they have already told something.
Nouns and adjectives.
Nouns end with "-o". For example, "patro means "father". To make a noun plural add -j. For example: "patroj means "fathers".
Adjectives end with "-a", adverbs end with "-e", for example "granda means "big", "bona means "good", "bone" means "well".
The "-n" ending is the mark of the direct object (the Accusative case) in nouns and adjectives. For example:
In adjectives and adverbs is comparison made by words "pli" ("more") and "plej" ("most"). For example:
Pronouns.
So, to say how old somebody is in Esperanto, just say:
Verbs.
Verbs end with "-as" when they are in present tense. English uses "I am", "you are", "he is". But in Esperanto, there is just one word for "am", "are", "is" - "estas". Similarly, "kuras" can mean "run" or "runs". Infinitives end with "-i". For example, "esti" means "to be", "povi" means "to can". It is easy to make past tense - always add "-is" ending. To make future tense, add "-os". For example:
Many words can be made opposite by adding "mal" at the beginning.
Examples of sentences which show the rules:
Yes/No questions.
To make a yes-or-no question, add "Ĉu" at the beginning. For example:
Unlike in English, they can answer to a yes/no question only "jes" (yes) or "ne" (no).
Numbers.
The numbers are:
Numbers like twenty-one (21) are made by their compounding by order of magnitude. For example: "dek tri" means thirteen (13), "dudek tri" means twenty-three (23), "sescent okdek tri" means six hundred eighty-three (683), "mil naŭcent okdek tri" means (one) thousand nine hundred and eighty-three (1983).
Prefixes and suffixes.
Esperanto has over 20 special words which can change the meaning of another word. People put them before or after the root of a word.
These words combined can make very long words, such as "malmultekosta" (cheap), "vendredviandmanĝmalpermeso" (prohibition of eating a meat on Friday).
Prefixes.
Prefixes are added before the root of the word.
Suffixes.
Suffixes are added after the root of the word, but before the ending.