Two voice note-against-note counterpoint
By far the simplest form of counterpoint. This is because there is only two voices that move in tandem.
Fig.1 first species counterpoint
You can see that there are only two voices and they sing/play at the same time as the other. Most of the time, if not all of the time, in Baroque music, the composer will only use diatonic intervals. Chromatic intervals were treated as to dissonant and dealt with in very specific ways. The most harmonically-unstable interval (by Baroque definitions) is the tritone. The tritone is the interval of an augmented fourth, or diminished fifth. Baroque composers thought of this interval as evil because it is made up of six half-steps.
Fig.2 Tritones
Just remember that in first species counterpoint that there are only two voices that move in tandem. This creates a series of intervals and the intervals usually do follow the circle of fifths progression (I iii VI ii V I).
