osu! "hit"object understanding
Circle:
an object you click once, does not last in any form as you will most likely instantly leave it after you made said click
therefore suited for short, jabby notes and beats in the music rather than echoing ones as opposed to sliders
Slider:
an object you click once, then follow up to a certain point (preferably the end, though frequently slipped out of early due to mapping in different directions than where the slider is pointing.
features multiple hitsounds with just one click (-> passive hitsounds), resulting in pressure only on the first one (note: the longer the slider, the more the player switches from a "clicking mode" into a "hold mode", therefore the slider end gets more "powerful" in some cases; predominately used in easier difficulties, emphasizing strong beats with sliderends while keeping a simple clicking rhythm to naturally follow and introduce people to - personally, I find the threshold for this to be around 3/2 beat sliderlength but it greatly varies on the overall momentum and intensity of the song in question)
therefore, to emphasize multiple equally strong beats, you should not use one single slider (again, lower difficulties may be an exception due to beat density and more natural/easy clicking rhythms; note that in these cases, you should still make sure to respect beat patterning (-> start sliders on the first of such beats rather than the second as a 1-1-1-1 rhythm is much easier to note and follow than a 1-2-2-2 (-> you'd end up hitting every second beat then instead of every first, which in most cases is very quirky)))
ADDITIONAL HITSOUNDING (CAREFUL!! DANGEROUS!!): You may use a slider's end/reverse arrow/ticks to emphasize additional layers in the song which are not part of the front layer (which naturally, you should be mapping and always prioritize) - this is dangerous because it can be very hard to keep the actual clicking and playing rhythm/emphasis of the main beat and frontline if you are trying to emphasize and feature too many things at once, therefore you should always consider your priorities first before doing anyhting like this
Spinner:
no click required, which means no initial pressure from the player but a consistent, quick circular motion
therefore suited for windups and strong passages that do not have destinctly pressured or individual beats
NOT suited for soft outros or anything like that since, well, people will naturally try to spin them as fast as possible: super low volume outro != spinning 477SPM, wouldn't you think?