The lower card shows the chords that go with the tones in each key. The chords built on tones of a scale are often referred to by roman numerals, for example, the root tone is the I, the next tone in the scale is II (or ii, if the chord is minor), the fifth is V etc. Often, chord progressions are referred to by these numerals, like the Blues progression: I-IV-I-V-IV-I. In that way, you can discuss the functions of chords in a piece, independent of the key that it is transposed to.
The card shows you how to translate that back to concrete notes and chords in a given key. So when you're in the key of A major, you find the row that has "A" in the first column, and then look up the columns that have the right numbers. In this example, the Blues progression translates to A-D-A-E-D-E. If you want to play a blues in F, it would be F-Bb-F-C-Bb-F.
For each note in a key, you can build a triad consisting of the notes in the scale - the so-called diatonic chords. The card also shows you what kind of chord you get in major scales: without extra symbols next to the chord, you get a major chord. The "m" next to the note refers to minor triad. The "o" refers to diminished triads.