It all depends on the note you finish on. That is the tonic of the scale. Most often, it is also the note you start on.

(Yes, I know there are some exceptions)

If you finish on D, and play all the white notes, it is Dorian mode.
This sounds a bit like a minor key, and the final chord will be Dminor
Scarborough Fair and Drunken Sailor are well-known Dorian tunes

If you finish on D, and play all the notes of a scale of G, i.e. F# instead of F, you are in a different mode (mixolydian, I think).
The final chord will be DMajor

If you finish on D, but play the notes of a scale of F, you are in the Aeolian mode, and will again finish on a Dminor chord.
This is regarded as the 'natural' minor key, which was modified to make the modern minor.

Another way of looking at it is from the number of sharps or flats you add to the key signature.

C major has none
C Mixolydian has one flat (same notes as F major)
C Dorian has 2 flats (same notes as Bb major)
C Aeolian mode has 3 flats - the same as C Minor or Eb Major).

And so on

These are examples of a general rule
For example:
To get from the major to the Mixolydian, flatten one note in the key signature, either remove a sharp or add a flat, as appropriate

Major to Dorian - two notes are flattened
Major to Aeolian (or minor) - three notes are flattened.
etc.