Mi metas la ŝlosilon en mian sakon antaŭ ol mi iras al la laboro.

The -n marks the direct object of the verb.

Here, meti means to put/place, and the thing being put is la ŝlosilo → la ŝlosilon.

So:

• Mi metas la ŝlosilon = I put the key

In Esperanto, the direct object usually gets -n.

Because adjectives in Esperanto must agree with the noun they describe.

• mia sako = my bag
• mian sakon = my bag in a form that needs -n

Since sakon has -n, the describing word mian must also have -n.

So the pattern is:

• mia sako
• mian sakon
• la miajn sakojn, etc.

Agreement happens in number and case.

This is a very important Esperanto pattern.

• en mia sako = in my bag → location, no movement
• en mian sakon = into my bag → movement toward the inside

Because the sentence describes motion into the bag, Esperanto uses en plus the accusative (-n).

So:

• La ŝlosilo estas en mia sako. = The key is in my bag.
• Mi metas la ŝlosilon en mian sakon. = I put the key into my bag.

English often does not show this difference clearly, but Esperanto does.

Antaŭ ol means before when it introduces a whole clause.

Here it is followed by a full clause:

• mi iras al la laboro = I go to work

So:

• antaŭ ol mi iras al la laboro = before I go to work

A useful contrast:

• antaŭ la laboro = before work
• antaŭ ol mi iras al la laboro = before I go to work

So antaŭ alone can come before a noun phrase, but antaŭ ol is used before a verb clause.

It is the same word, but in antaŭ ol it is part of a fixed expression.

You may already know:

• pli granda ol = bigger than

But in:

• antaŭ ol
• post ol is not normally used the same way; usually just post kiam

the ol is not a comparison by itself. In antaŭ ol, just learn the whole phrase as before + clause.

So yes, it is the same word, but here it works inside a set construction.

Because Esperanto often uses the present tense for a habitual action or general routine.

So this sentence can mean something like:

• I put the key in my bag before I go to work
• I usually put the key in my bag before going to work

The present tense in Esperanto does not only mean right now. It can also describe what someone regularly does.

If you wanted a one-time past action, you could say:

• Mi metis la ŝlosilon en mian sakon antaŭ ol mi iris al la laboro.

If you wanted a future one-time action:

• Mi metos la ŝlosilon en mian sakon antaŭ ol mi iros al la laboro.

Al la laboro is a normal way to say to work.

• iri al la laboro = to go to work

Esperanto can also sometimes use -en for motion toward a place, and you may see forms like hejmen (homeward, home). But al la laboro is straightforward and very common.

Also, laboro literally means work, not necessarily the physical workplace. In this expression, it works much like English go to work.

If you wanted to emphasize the workplace as a location, you might use another word such as laborejo in some contexts.

Because the speaker means a specific key: the key.

Esperanto uses la much like English uses the.

So:

• ŝlosilo = a key / key
• la ŝlosilo = the key

In this sentence, it sounds like the speaker has a particular key in mind, so la is natural.

This is one of those places where Esperanto and English do not match exactly.

English often drops the article in fixed expressions:

• go to work
• go to school
• be at home

Esperanto does not always copy that pattern. Al la laboro is a very natural way to say to work.

So even though English says to work, Esperanto often uses al la laboro.

This is best learned as a normal expression rather than translated word-for-word.

Yes. Esperanto word order is fairly flexible because endings show grammatical roles.

The given sentence uses a very neutral, common order:

• Mi metas la ŝlosilon en mian sakon antaŭ ol mi iras al la laboro.

But other orders are possible for emphasis, for example:

• Antaŭ ol mi iras al la laboro, mi metas la ŝlosilon en mian sakon.

That version emphasizes the time relationship first.

Still, for learners, the original order is a good default: subject + verb + object + other information.

It can mean any of those, depending on context.

Esperanto present tense -as does not force the distinction that English makes between:

• I put
• I am putting
• I do put

So mi metas can mean:

• I put
• I am putting
• I place

In this sentence, because of the whole context, it most naturally sounds like a routine action: I put the key in my bag before I go to work.

A few helpful points:

• ŝ sounds like English sh
• ŝlosilo begins roughly like shlo-
• aŭ is a diphthong, roughly like the ow in cow

So:

• ŝlosilon ≈ shlo-SEE-lon
• antaŭ ≈ an-TOW

Also remember that Esperanto stress normally falls on the second-to-last syllable:

• ŝlo-SI-lon
• an-TAŬ
• la-BO-ro

That regular stress pattern makes pronunciation much easier than in English.