To start let us take a look at the very first verse of the Bible, which along with the rest of the non-Deuterocanonical Old Testament was translated by the creator of Esperanto, L. L. Zamenhof.
Here are some things to notice:En la komenco Dio kreis la ĉielon kaj la teron. Genezo 1:1
1. Nouns. There are four nouns in this verse: komenco, Dio, ĉielon, teron. You will notice that two end in -o. This shows that they are nouns. The second two end in -on. The -o shows they are nouns, and the -n shows that they are in the accusative case. This is a fancy way of saying that those nouns are on the receiving end of the action of a verb. What verb? Kreis, which means 'created.' What is being created? La ĉielon kaj la teron--- the heaven and the earth.
2. Subject of the sentence. Who is the subject of the sentence? Dio--- God. God is the one doing the creating. So the noun 'God' is in the nominative case. Which is another way of saying that it's God doing the action of the verb kreis.
3. Verb. The verb kreis is in the past tense. The past tense of a verb is marked by the ending -is. The infinitive of the verb kreis is 'krei.' Krei means 'to create.' In English we show the infinitive of a verb with the word 'to.' In Esperanto we show it by the ending -i.
4. En la komenco. The word 'komenco', which means beginning, is not the subject of the sentence. The 'komenco' is not creating anything. But it is not being created, either. In the phrase 'en la komenco', you do not need to add -n because it is not the direct object of the verb--- it's not receiving the action of the verb 'created' so it is not in the accusative case.
5. For extra practice, you might want to copy the Esperanto text above into a notebook. Also copy the verse in English translation--- or whichever language you speak well. Look up any Esperanto words you don't know well in an online Esperanto dictionary.
Do you understand?
Kiu kreis la ĉielon?
Dio kreis la ĉielon.
Kiu kreis la teron?
Dio kreis la teron.
Ĉu la komenco kreis Dion?
Ne, la komenco ne kreis Dion.
The next two verses of the first chapter of Genesis.
2 Kaj la tero estis senforma kaj dezerta, kaj mallumo estis super la abismo; kaj la spirito de Dio ŝvebis super la akvo.
Jesus Army Multilingual Bible, Esperanto: http://jesus-army.com/bible/Esperanto/1