The Ionian mode is the “modal equivalent” of the major scale: its intervals are the same but the notes of the scale are treated differently. In particular it changes the relation between melody and harmony; if tonality has its meaning in the use of cadences and harmonic functions, we can say that in modality the melody is treated more freely.
Here you can find the fingerings of the scale, limited to one and two octaves. Black dots are the notes of the triad on the first degree (1, 3 and 5 scale degrees), while white dots are the other notes of the scale. The arrows show the possibility to play some notes on a different string.