On each of these lines are placed letters to represent notes. If an eighth were used, it would appear in the same place, but with a line above it. It does in fact represetnt a trill. The exact form tof the trill is not known, but it did appear to have a specific meaning. Generally, one just trills with the note in the scale above the note in question.
Timing is fairly straight forward.
The duration of a note is determined by the time indicator above it. If there is no time indicator above a note, its duration is equal to that of the last note. For notes that last one and a half times as long as normal, a dot is added to the side of the time indicator, as in normal sheet music. In this case a semi-breve is a 1, a minim is a 2, a crotchet is a 3 etc. French tablature was not universally written in this way, and a number of minor variations are worth noting.