Ŝi ridis, kiam ŝi vidis min kun granda ĉapelo, longaj ŝtrumpoj kaj tro grandaj botoj.

Because min is the direct object of vidis.

• mi = I
• min = me

In Esperanto, the direct object gets -n. So:

• ŝi vidis min = she saw me

If you said ŝi vidis mi, that would be ungrammatical.

Because Esperanto normally states the subject clearly in each clause.

Here there are two clauses:

• Ŝi ridis = she laughed
• kiam ŝi vidis min... = when she saw me...

Even though it is the same person in both clauses, Esperanto usually keeps the pronoun instead of leaving it out.

Kiam means when. It introduces a time clause.

So:

• Ŝi ridis, kiam ŝi vidis min... = She laughed when she saw me...

It can mean at the time that or when, depending on context.

Because Esperanto commonly uses commas to separate main clauses from subordinate clauses.

So the comma in:

• Ŝi ridis, kiam ŝi vidis min...

is completely normal. Esperanto punctuation is often a bit more regular here than English punctuation.

Because one preposition can govern a whole list.

So kun applies to all three items:

• kun granda ĉapelo
• (kun) longaj ŝtrumpoj
• (kun) tro grandaj botoj

This is just like English with a big hat, long stockings, and overly large boots.

Because they are objects of the preposition kun, not direct objects of the verb.

The direct object is only:

• min

After a preposition like kun, nouns normally do not take the accusative -n.

So:

• vidis min → direct object, so min
• kun granda ĉapelo → after a preposition, so no -n

Because adjectives must agree with the nouns they describe.

• ĉapelo is singular, so granda
• ŝtrumpoj is plural, so longaj
• botoj is plural, so grandaj

In Esperanto:

• singular adjective: no -j
• plural adjective: add -j

So:

• granda ĉapelo = a big hat
• longaj ŝtrumpoj = long stockings
• tro grandaj botoj = too-big boots

No. Tro means too, in the sense of excessively.

So:

• tro grandaj botoj = boots that are too big

If you wanted very big, you would usually say:

• tre grandaj botoj = very big boots

This is an important difference:

• tre = very
• tro = too / excessively

Esperanto often uses kun (with) to express that someone has something on them or is wearing it, especially when the context is clear.

So:

• ŝi vidis min kun granda ĉapelo...

naturally means that she saw me with / wearing a big hat, long stockings, and too-big boots.

A more explicit wording is possible, but this sentence is perfectly normal.

In normal reading, it describes me.

The structure is:

• ŝi vidis min kun... = she saw me with...

So the natural meaning is that I was the one with the hat, stockings, and boots.

In theory, some prepositional phrases can be ambiguous in many languages, but here the intended reading is very clear from context.

Because Esperanto does not use la unless the speaker wants to mark something as definite.

Here the sentence is simply describing what I was wearing:

• granda ĉapelo
• longaj ŝtrumpoj
• tro grandaj botoj

That works fine without la. English also often does this in descriptions: with a big hat, long stockings, and oversized boots.

A learner often notices these right away:

• ŝ sounds like English sh
  • ŝi, ŝtrumpoj
• ĉ sounds like English ch
  • ĉapelo

So:

• Ŝi sounds roughly like shee
• ĉapelo starts with a ch sound
• ŝtrumpoj starts with shtr-, which may feel unusual at first for English speakers

These letters always have the same sound, which is one of the nice things about Esperanto spelling.