Going to

Going to: present continuous

We use the present continuous form of the verb go + preposition to + noun phrase to talk about movement in relation to a place or a person in the present:

Are you going to Maggie’s party tonight?

I’m going to the shops. Do you want anything?

Going to: future

We can use a present form of be + going to + the base form of a main verb to talk about the future. We use it for plans and intentions, predictions and commands:

I’m going to buy a new car next week. (plan or intention)

You’re not going to do all this in an hour. There’s just too much to do. (prediction: the speaker can see how much there is to do)

I’m telling you, you’re going to do it. You don’t have a choice. (command)

Was going to

We use a past form of be + going to when we talk about a plan we had that may have changed.

Compare

A: You’re not staying out in this rain, are you? B: Well Iam going to, yes.	B definitely intends to stay out in the rain.
A: You’re not staying out in this rain, are you? B: Well Iwas going to, yes.	B intended to stay out but may have changed his mind.