Not a stupid question at all .....
Keep to fairly standard ranges for your composition and you're unlikely to go wrong, so approx -
soprano -  middle C to A above the stave
alto -  F below middle C to D or E towards the top of the treble stave
tenor  -  C below middle C to G above middle C
bass  -  F below the bottom line of the bass stave to about middle C or D.
You will meet people who will be able to sing outside those limits, eg basses who can sing below F, or sopranos who can go way above A, altos who can sing a G or an A. But these are fairly safe workable ranges which will be useful to keep in mind.
Hope this is useful.
Male singers should be able to do a little more than this at top end. Basses are regularly asked to sing an F, F#