Arpeggios are a real mainstay of trance music. Essentially arpeggios are chords, but the notes are played individually either in ascending or decending order, sometimes both.
In the early days of synthesizers when most were monophonic (able to only play one note at a time), arpeggios enabled these synths to sound chords or chord progressions.
As we see advances in music technology, most Digital Audio Workstations will have an arpeggio function which can help quickly sculpt an arpeggio, but for the best ones, you’re going to have to get your hands dirty with the Editing tool.
Variations in arpeggios really add interest and can also help bridge into the next chord. It can be easier to work out a chord progression first, then split the chords up into their individual notes before making and adjusting any variations.