"I have to be at the airport at two."
Translation:Tengo que estar en el aeropuerto a las dos.
It is routine in spanish to say "en la estación", "en la fiesta", "en la universidad", and on and on to mean "at the station", "at the party", "at the university", and nearly any place else.
Although "A" can mean "at", it is seldom used alone for that meaning except to indicate a specific time. Like "A las ocho" to mean "at eight o'clock".
"A" is most often used for "to" and to connect certain verbs and many common phrases like "a diario" or "a la izquierda", and the infamous personal A.
so - in this lesson we are given the sentences 'ellos llegan al aeropuerto' and 'esos taxis van al aeropuerto' but apparently 'tengo que estar al aeropuerto' is wrong and has to be 'en el aeropuerto' I don't really understand - arriving at the airport = al and going to the airport = al but being at the airport = en el ??
It's because llegar and ir are linked verbs which use the preposition 'a' after them. Unfortunately, linked verbs use all sorts of different prepositions and are just something you have to rote learn.
In conjunction with all this, llegar means not just 'to arrive', but 'to arrive TO'. Similarly, ir also means 'to go TO'.
The last thing about this is simply that, shown here without the contraction for illustrative purposes only, your sentence is 'Tengo que estar a el aeropuerto', which translates as 'I have to be to the airport', which just sounds weird (in both languages).
In fact, it's by showing this that you can see why ir and llegar are linked verbs in the first place!