you would use -es when a word ends in a -ch like rich or glitch you use the ending -es
When speaking the Spanish language, the word es in Spanish means is. It would not be a proper sentence if you just use es. If using the Spanish word es in a sentence, you would need a verb and a noun to make it a good sentence.
Removing the "es" ending in "illnesses" would change the word to "illness," which refers to a singular instance of being unwell. The plural form "illnesses" denotes multiple instances or types of being unwell.
Add "s" to the end of a verb (e.g. run -> runs) for third person singular subjects (he, she, it). Add "es" to the end of verbs that end in s, sh, ch, x, or o (e.g. pass -> passes, watch -> watches).
Normally, you can use the word "sólo" for "just". "Is" in this case, without context would probably be "es". So..."sólo es" is what you are looking for.
You would use s and not es, but this is not the way to make the word plural. You would use apostrophe s to indicate possession. For example, the child's illness had the whole family worried. The plural of child is children.
Es-tu (un) étudiant ? (masc.) Es-tu (une) étudiante ? (fem.). We would not usually pronounce the articles un or une. And we would use the word "étudiant" only for someone at university level (use "élève" otherwise).
Rico has two meanings; means rich and in an informal way it means very tasty. Examples: "Pedro es rico" "Peter is rich." but if you say " Eso esta rico" ; it would mean " That is delicious or tasty''(slang)
When used before the word you are speaking of, it would be "buen". Example: Éste es un buen hombre. (This is a good man). In isolation, you would use "bueno". When used after the word being modified, you would use "bueno" or "buena". Example: La mujer es una persona buena. (The woman is a good person).
"La vida es una lucha" is the correct statement. Life is a struggle. The word "lucha" is a feminine word therefore you would use the feminine article "una" rather than the masculine counterpart, "un".
bodily
First, a person would likely ask you "¿Cuándo es tu cumpleaños?" to ask "When is your birthday?" To that, you would respond "Mi cumpleaños es..." and then the date. You use the singular verb "es" because birthday is a singular day (even though the word here looks plural). Por ejemplo: ¿Cuándo es tu cumpleaños? Mi cumpleaños es el treinta de marzo.
You would use 'es', a conjugation of the French verb 'etre'. So you could say: Elle es (she is). Il es (he is, it is). For other forms like 'are' and 'am', you could look up a conjugation chart for 'etre'.