Learn Dutch: De appel is lekker. - The apple is tasty.

To make a yes/no question in Dutch, you swap the order of the subject and the verb. This is called inversion. For this sentence, you move the verb is to the front, before the subject de appel. This gives you: Is de appel lekker? (Is the apple tasty?).

The current lesson is about dropping the '-t' in questions. Does that happen here?

Not in this exact sentence, because de appel acts as a third-person "it", so the verb remains is. The rule about dropping the -t only applies to the "you" form (jij or je). If you asked "Are you tasty?", the normal statement is Jij bent lekker, but as a question the -t from bent is dropped: Ben jij lekker?

Why is it just lekker and not lekkere?

Because the adjective comes after the noun and the verb is. When an adjective describes a noun but is separated from it by a verb like "to be", it never gets an extra -e at the end. You only add the -e if it comes directly in front of the noun, like in de lekkere appel (the tasty apple).

Does lekker only mean "tasty" for food?