Learn Hardcore Japanese: watasi ha asita kuukou ni ikimasu.

は is the topic marker, showing that 私 (I) is what the sentence is “about.” In English we say “As for me, tomorrow I will go…” whereas が would mark a new or emphasized subject (“It is I who will go…”). Omitting a particle after 私 would be ungrammatical here, because Japanese needs a marker to link 私 to the rest of the sentence.

Why is the time expression 明日 placed before the location 空港に?

Japanese word order for adverbials typically goes:

Time (when)
Place (where)
Manner/object (how/what)
Verb (action)
So 明日 (“tomorrow”) comes first, then 空港に (“to the airport”), then the verb 行きます. This order is flexible for emphasis, but time->place->verb is the default.

Why is 空港 followed by に instead of を or で?

With movement verbs like 行く (“to go”) you use に to mark the destination.

を marks a direct object (“I eat an apple”) – not a destination.
で marks the location of an action (“I study at school”), not the endpoint of movement.

Can I use へ instead of に after 空港? What’s the difference?

Yes. 空港へ行きます is also correct. へ indicates direction (“toward the airport”), while に is more exact about arriving at that place. In everyday speech both are interchangeable for “go to.”

Why does the sentence end with 行きます instead of the plain form 行く?

行きます is the polite non-past form (the –ます form), suitable for most conversations, especially with strangers or superiors. The casual/plain form is 行く, so in an informal context you’d say 明日空港に行く.

What is the function of ます in 行きます?

–ます is a polite suffix attached to the verb stem (行き-). It makes the statement more polite. It doesn’t add tense; the non-past vs. past distinction comes from the ending (ます vs. ました).

Why is there no です at the end? Doesn’t polite Japanese usually end with です?

In Japanese the copula です attaches only to nouns and adjectives (e.g. 元気です, 学生です). Verbs use –ます instead. So for “I am a student” you need です, but for “I go” you use 行きます, not 行きますです.

Do I have to include 私? Could I just say 明日空港に行きます?

You can drop 私 because Japanese often omits pronouns when the subject/topic is clear from context. 明日空港に行きます still clearly means “I will go to the airport tomorrow” if the listener knows you’re talking about yourself.

Japanese has no articles like the or a. How do I know whether 空港 means “the airport” or “an airport”?

You rely on context. If you and your listener know which airport you mean (e.g. the one you usually use), it’s understood as “the airport.” If you’re speaking generally, it can mean “an airport.” There’s no separate article word in Japanese.