Learn Spanish (Latin America): ¿La propina está en la mesa?

Está comes from the verb estar. In Spanish, you always use estar (rather than ser, the other verb for "to be") when talking about physical location—even for inanimate objects like a tip (la propina) resting on a table (la mesa).

I thought en meant "in". Why does it translate to "on" here?

The word en is a multitasker! It can mean "in", "on", or "at" depending on the context. Since you would normally leave a tip on a table rather than inside it, context tells us it means "on" in this sentence.

The English translation starts with "Is", but the Spanish sentence starts with "The tip". Why isn't it ¿Está la propina...?

In Spanish, you don't have to change the word order to ask a yes/no question. You can simply take a normal statement like La propina está en la mesa (The tip is on the table) and add question marks and a rising tone of voice. Swapping the words to ¿Está la propina en la mesa? is also perfectly correct and common, but not required.