La ŝraŭbingo estas sub la selo.

La is the Esperanto definite article, equivalent to English the. It is used here because the sentence refers to specific things: a particular ŝraŭbingo and a particular selo.

A useful point: la never changes. It stays la for singular, plural, subject, and object.

In Esperanto, nouns normally end in -o. So both ŝraŭbingo and selo are nouns.

Some related forms:

• -oj = plural
• -on = singular direct object
• -ojn = plural direct object

In this sentence, both nouns are singular, and neither one is a direct object.

Estas is the present-tense form of esti, meaning to be.

Esperanto verbs do not change depending on the subject, so:

• mi estas = I am
• vi estas = you are
• li estas = he is
• la ŝraŭbingo estas = the screw-holder/socket is

So estas is simply the normal present-tense verb here: is.

Sub is a preposition meaning under or below.

It introduces a place phrase:

• sub la selo = under the saddle

So in the sentence, sub la selo tells you where the ŝraŭbingo is.

Because this sentence describes a location, not movement.

In Esperanto, after a preposition, you usually use the basic noun form:

• sub la selo = under the saddle

The -n ending can be used with a preposition when there is movement toward a place:

• Mi metas ĝin sub la selon = I put it under the saddle

But here nothing is moving. The sentence only says where something is, so sub la selo is correct.

It is a compound word:

• ŝraŭb- = related to ŝraŭbo, meaning screw
• -ing- = a holder, sheath, socket, or container-like part that something fits into
• -o = noun ending

So ŝraŭbingo literally suggests something like a screw-holder or screw-socket. In technical vocabulary, Esperanto often builds words this way.

A few key points:

• ŝ sounds like English sh
• aŭ is a diphthong, roughly like ow in cow
• g is always hard, as in go
• stress in Esperanto falls on the next-to-last syllable

So:

• ŝraŭbingo is pronounced roughly shraow-BIN-go
• selo is SE-lo

The beginning ŝr- may feel unusual to an English speaker, but you just pronounce both sounds: sh + r.

This is the most neutral and common order:

La ŝraŭbingo + estas + sub la selo

That is basically:

• subject
• verb
• place phrase

Esperanto word order is fairly flexible, so other orders are possible for emphasis, such as Sub la selo estas la ŝraŭbingo, but the original sentence is the plainest and most natural way to say it.

Because the sentence refers to one ŝraŭbingo and one selo.

If you wanted the plural, you would add -j:

• la ŝraŭbingoj = the screw-holders/sockets
• la seloj = the saddles

So the absence of -j tells you both nouns are singular.

Sometimes yes, but it would change the feel of the sentence.

Using la makes the nouns definite and specific:

• La ŝraŭbingo estas sub la selo = the specific screw-holder/socket is under the specific saddle

Without la, the sentence would sound less specific and often less natural unless the context clearly calls for an indefinite or more general meaning.

Also, Esperanto has no separate word for a/an, so the language often uses either la or no article at all, depending on the meaning.