What is it?
The Future Tense is used to refer to a future event. Something that hasn't happened yet.
The Rules
To express future tense in Danish you would use the verb at ville (will) or at skulle (shall).
Be mindful that we are talking about a future sense of 'will' not the 'desire-to-do-something will' nor the 'have-to-do-something shall'.
Therefore I will do it tomorrow is jeg vil gøre det i morgen.
[verb (present tense)] + [time adverbial]
In fact you rarely see Danes today using the future auxillary verb vil. It is adding little words like 'tomorrow' and 'yesterday' or 'one day' and so on that we can see that we are talking about the future and not the present.
Examples
The equivalent to I will come tomorrow in Danish would simply be Jeg kommer i morgen. So the active Present Tense of komme is used to describe the future event.