An AdSlot is always assigned to a specific AdSchedule. Here you store all the information relevant for banner delivery in the "AdSlot configuration", including the assignment of the assets, their runtimes, target URLS and ad/creative/banner names.
In order to be able to store assets as ads in an AdSlot, you must have uploaded them in advance to the Asset Library.
Several AdSlots with identical runtimes can be assigned to an AdSchedule in order to define rotators. Any other runtimes can be defined, for instance, if one AdSlot takes over another. The runtimes are only limited by the total runtime of the AdSchedule or better said the plan item of your Mercury planning from which it was created.
AdSlots can be easily distinguished from Click-Trackers, as these do not have a symbol on the right-hand side, while Click-Trackers have a lock symbol here.