Use the adverb assuredly when you're positive something is true. If last year was difficult, you might believe the next year will assuredly be much better.
This word is frequently used as a sentence adverb, to emphasize how absolutely certain you are. "Assuredly, we will have a lot of trick-or-treaters on Halloween," you might say as you buy 15 bags of candy. You can also use it to mean "confidently," like when your unflappable cousin steps assuredly onto the stage to deliver a graduation speech to an audience of hundreds.