a) ​I'm having lunch with Josie tomorrow.

b) I'm going to have lunch outside today because the weather's lovely.

Explain the difference in meaning, if any.

a) ​I'm having lunch with Josie tomorrow.

b) I'm going to have lunch outside today because the weather's lovely.

Explain the difference in meaning, if any.

​Both are used for future plans, but the Present Continuous is specifically about an arrangement with another person.

a) ​Which platform does the train leave from?

b) The train will be leaving soon. Hurry up!

Explain the difference in meaning, if any.

a) ​Which platform does the train leave from?

b) The train will be leaving soon. Hurry up!

Explain the difference in meaning, if any.

​The Present Simple is used for a timetabled or scheduled event; the Future Continuous is used here to talk about what the speaker expects to happen in the normal course of events (trains usually leave when expected)

a) ​Sorry about breaking your favourite mug. I'll buy you a new one, I promise.

b) I'm going to buy a new coat this afternoon.

Explain the difference in meaning, if any.

a) ​Sorry about breaking your favourite mug. I'll buy you a new one, I promise.

b) I'm going to buy a new coat this afternoon.

Explain the difference in meaning, if any.

​Will is used to describe a decision at the moment of speaking (the speaker didn't know beforehand that they would break the mug); be going to describes an action which has already been planned or decided.