Surely, Certainly, Without Exception, Always, Definitely
adverb
This word looks like a verb but it's not (sorry!). It's an adverb. The kanji itself means certain and the vocab version means all sorts of variations on that: surely, certainly, and without exception to name a few.
かならず
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you: Ra, the Egyptian god asks you: "Can you do it? Are you certain you can build the pyramids?" "Yes I can ra (かなら). Yes I can," you reply.
必ず毎日歩くことが大切です。
It is important to make sure to walk every day.
次のクラスは、必ず来てください。
Please be sure to come to the next class.
死ぬ前に、必ずワニカニをコンプリートします。
I'll surely complete WaniKani before I die.