A slash section is uses when you want to give leberty to improvise to the performer. The slashes in the measuers follow the meter, and there are chords indications above some slashes to indicate which notes to use for improvisation.
The slash section will replace the previous content, not taking into account of pitches, rests or durations.
If you want more granularity on the rhythm of the slashes, you can use the rhythmic notation instead.
The rhythmic section will replace the previous content by slashes, but will keep the durations and rests.
When you are in the rhythmic mode, you can add/remove slash the same way you are adding notes, and you can change the notes/slashes durations.