A playlist is a list of tracks with a rule attached: when it plays, how often, and in what order. Together they form the rotation your station draws from when nobody is live.
Four playlists with their play mode and time window
The four things you set
Name and tracks — what it's about.
Play mode. Random shuffles the list. In order plays it top to bottom. Ascending tempo builds up, which works nicely in a morning block.
Weight. If several playlists are eligible at the same time, the weight decides how often each takes a turn. A list with weight 2 comes round twice as often as one with weight 1. That's how you make your A-list return more often without throwing away your B-list.
Time window. By default a playlist runs all day. Set a window from 06:00 to 10:00 and it only takes part then. That way your morning sounds different from your night without you switching anything.
The window is both fields or neither. Filling in one time produces a list that never gets its turn.
Jingles are a playlist too
You set a jingle playlist to every N tracks. The screenshot shows "Elke 6 nummers": after every six records an ident drops in. That's the normal way to keep your station recognisable.
Watch out, because this is the trap most questions are about: while an hour layout is running, these jingle rules do not apply. The layout then decides where the idents fall. If you notice your idents have "disappeared", first check whether an hour layout is active.
Each track once
Within a playlist every track plays once before the list starts over. That's deliberate: a listener who hears the same thing twice in an hour thinks something is broken.
How many tracks?
Enough that a listener doesn't notice. An hour of listening is about fifteen records; if you want someone to listen all afternoon without repeats you're quickly at a hundred. Below twenty a regular listener hears the whole rotation within a day.