Learn Turkish: Telaşla tren istasyonuna yetişmesi lazımdı. - He had to make it to the train station in a rush.

To say someone 'had to' do something in Turkish, we combine a short verbal noun (an action word ending in -me or -ma), a possessive ending to show who had to do it, and the past tense word lazımdı (it was necessary). Here, we have the verb yetişmek (to make it in time). We drop the -k to get the short form yetişme, add the third-person possessive -si (his/her), and then add lazımdı. Literally, it translates to 'His making it in time was necessary.'

Could I just use gitmesi lazımdı (he had to go) instead of yetişmesi lazımdı?

You could, but it changes the meaning slightly. Gitmek just means 'to go', whereas yetişmek implies a sense of urgency, meaning 'to catch', 'to reach', or 'to make it somewhere in time'. Since he was in a rush (telaşla), yetişmesi is the perfect word choice here.

Why is there an -n- in the middle of istasyonuna?

The phrase for 'train station' is tren istasyonu, which is a noun compound linking two nouns together. The -u at the end is the possessive suffix that glues them. When we want to add the direction suffix -a (to) to a word that already ends in a possessive suffix, Turkish requires the buffer letter -n- instead of the usual -y-. So it becomes istasyonu + n + a.