Learn Turkish: Parkta bekle. - Wait in the park.

The dictionary form of 'to wait' is beklemek. To give a command to one person (an informal 'you'), you simply remove the -mek ending. This leaves the bare verb root, bekle, which means 'wait!'.

I learned that 'in' or 'at' is -da or -de. Why does it say parkta here?

The location suffix is usually -da or -de. But Turkish has a consonant harmony rule where soft consonants change to hard consonants to match the word they attach to. Because park ends in a hard k sound, the d changes to a t, making the ending -ta.

Can I include sen (you) in this sentence?

Yes, you could say Sen parkta bekle, but the pronoun is usually left out unless you want to emphasize exactly who should wait (like saying 'YOU wait in the park, and I will go inside'). Without sen, the command bekle already clearly means 'you'.

Why is the location placed before the verb?

Turkish usually puts the verb at the very end of the sentence. Since the subject ('you') is dropped here, the sentence simply starts with the location (parkta) and ends with the action (bekle).