Much baroque music features a special part called the basso continuo. In this part, a bass line is written and performed by a bass instrument, such as a cello or organ.
Above or below each note are Arabic numerals. This is called figured bass. The numerals indicate the intervals to be performed above the written note. These notes are played by some kind of chordal instrument, like a lute or harpsichord (or an organ again.) In common practice, each possible inversion of a triad is notated with a set of intervals unique to that inversion. Learn these thoroughly.
A root-position triad gets no special notation besides its Roman numeral.
A first inversion triad is notated with a superscript 6.
A second inversion triad is notated with a 6 and 4.
A root-position seventh chord is notated with a superscript 7.
A first inversion seventh chord is notated with a 6 and 5.
A second inversion seventh chord is notated with a 4 and 3.
A third inversion seventh chord is notated with a 4 and 2.
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