Infano ne estas matura homo.
La infano jam ne ploras.
La ĉielo estas blua.
Kie estas la libro kaj la krajono?
La libro estas sur la tablo kaj la krajono kuŝas sur la fenestro.
Sur la fenestro kuŝas krajono kaj plumo.
Jen estas pomo.
Jen estas la pomo, kiun mi trovis.
Sur la tero kuŝas ŝtono.
1. NE is used in the same way as the English not; except, it always precedes the word it "denies". It can also stand alone, in which case it is the same as the English no.
2. As well as being connected to a noun by estas, an adjective (word ending in -A) can be associated directly with its noun (matura homo).
3. JAM NE -AS = is no longer -ing, has stopped -ing.
4. KIE = where is one of a set of words known as correlatives. Each of these words starts with a letter or group of letters describing its function (KI- a question or linking word) and a letter or group of letters describing the type of information to which it refers (-E -> place, location). It is probably easier to learn to generate these words as you need them than it is to simply memorize them (I never did succeed in learning their Latin equivalents by heart). A similar word in this exercise is KIUN, where -U -> selection out of a group (the -N on the end is something completely different).
5. JEN is a word that you use when you want to point to something; consider it the verbal equivalent of throwing out your arm toward the thing you are describing. It is usually used with ESTAS or some other verb (Jen estas libro, jen kuŝas krajono), but some people simply drop the verb, and this is not considered incorrect (Jen libro, jen krajono).
6. -IS on the end of a word indicates that the word describes some sort of state or action which has already ended, or at least is of no further importance. In other words, it marks a verb in the past tense. Compare this with -AS in #5.