I just say "remind me to do this on X day at X time"....google now creates an alarm that reminds me. Otherwise I use Keep for notes that is supported by google now as well.
Unfortunately Google decided to bury reminders in Google Now, rather than having a separate app. Weird, since they seem to have a separate app for everything else.
Also seems to be a bug where a reminder set by voice will not always cause an audible/vibrate alarm... so if I don't see it in notifications or menu bar I may miss it. I believe the fix is to tap the onscreen button to set the alarm, rather than verbally replying yes.
That said I do use Google Now for setting quick reminders. I just can't seem to "trust" it 100%.
Mike