Short answer - future tense.
How about going out?
This is a question, and you are proposing to go out in the future - possibly the immediate future, possibly later, but either way you haven't begun "to go" out yet, so it can only be in the future. Also, the tense is conditional - it depends if the person you ask agrees.
I can see your confusion - many verbs ending with -ing are the present tense, for example:
- I will dig a hole (future)
- I am digging a hole (present)
- I dug a hole (past)
Remember though that the present tense of many verbs also describes an ongoing or continuous action. Let's say that digging a hole will take 4 hours and you want to tell someone that you will busy with this all afternoon - you would say:
I will be digging a hole all afternoon.
That shows that the future action of digging will be ongoing throughout the afternoon. If you simply said "this afternoon I will dig a hole" it does not carry the same information as to how long it will take.
Likewise there are other ways of saying you are going somewhere in the future:
- I am going out tonight
- I will be going to the party
Both of these are conditional on either it being a specific time of day or the correct time for a specific event.