tenin ha gaikokuzin ni kippu no kaikata wo setumeisuru to omoimasu.

は marks 店員 as the topic of the sentence: as for the clerk...

So the sentence is organized like this:

• 店員は = As for the clerk
• 外国人に = to the foreigner
• 切符の買い方を = how to buy a ticket / the way to buy a ticket
• 説明すると思います = I think (they) will explain

Using は often gives a more general or topical feel. It is not just identifying who does the action, but setting up the clerk as the person being talked about.

If you used が instead, it would sound more like you are specifically identifying the clerk as the one who will do the explaining.

With 説明する, the pattern is often:

• person receiving the explanation
  • に
• thing being explained
  • を

So:

• 外国人に = to the foreigner
• 切符の買い方を = the ticket-buying method / how to buy a ticket
• 説明する = explain

This is similar to English explain something to someone.

So に marks the target/recipient of the explanation.

切符の買い方 is a noun phrase meaning:

• the way to buy a ticket
• more naturally in English, how to buy a ticket

Breakdown:

• 切符 = ticket
• 買い方 = way of buying / how to buy
• の links them together

Here, の works like of or a possessive-type connector in English. It connects ticket to way of buying, so the meaning becomes:

• ticket’s way of buying
  which we naturally translate as
• the way to buy a ticket

This noun + の + noun pattern is extremely common in Japanese.

買い方 is a set grammar pattern:

• verb stem + 方（かた） = way of doing something

Examples:

• 食べ方 = way of eating / how to eat
• 使い方 = way of using / how to use
• 読み方 = way of reading / how to read
• 買い方 = way of buying / how to buy

For 買う, the verb stem is 買い, so:

• 買う → 買い → 買い方

買う方 would not mean the same thing. 方 can also be read ほう and mean side, direction, or one/person who..., so 買う方 would be interpreted differently.

Here, the correct pattern is definitely 買い方（かいかた）.

In Japanese, を does not only mark physical objects. It marks the direct object of many verbs.

With 説明する, the thing being explained takes を:

• 何を説明する = explain what?

So here:

• 切符の買い方を説明する = explain how to buy a ticket

Even though 切符の買い方 is an idea or piece of information, it is still the thing being explained, so を is correct.

Here, と marks the content of what is thought.

Structure:

• 説明する = will explain / explain
• と = that
• 思います = think

So:

• 説明すると思います = I think that (someone) will explain

This と is often called the quotation or complement particle. It attaches to a plain-form clause and turns it into the content of thought, speech, etc.

Examples:

• 行くと思います = I think (someone/I) will go
• 難しいと思います = I think it is difficult
• 先生だと思います = I think it is the teacher

Before と, Japanese normally uses the plain form, not the polite ます form.

So:

• 説明する
  • と思います = correct
• 説明します
  • と思います = normally not used in standard grammar

This is very common:

• 行くと思います
• 高いと思います
• 学生だと思います

Even though the final verb 思います is polite, the clause before と stays in plain form.

Japanese often leaves that ambiguous unless the context makes it clear.

So this sentence could mean things like:

• I think the clerk will explain to the foreigner how to buy a ticket.
• I think a clerk will explain to a foreigner how to buy a ticket.
• I think clerks explain to foreigners how to buy tickets.

The exact interpretation depends on context.

Because Japanese has no articles like a or the, and nouns usually do not show singular/plural clearly, you often have to rely on the situation.

Usually yes, but in natural Japanese it can also sound like a softened statement, not just a report of your inner thoughts.

So 説明すると思います can mean:

• I think they will explain
• They will probably explain
• My guess is that they’ll explain

Japanese often uses と思います to sound less direct or less forceful than making a flat statement.

So compared with:

• 説明します = They will explain.
• 説明すると思います = I think they will explain / They will probably explain.

The second one sounds a bit softer and less absolute.