• 確認かくにん — confirmation
• 確実かくじつ — certainty
• 正確せいかく — accurate
• 確保かくほ — secure; obtain
• 確率かくりつ — probability
• 確信かくしん — conviction; confidence

The kanji 確 is made up of 石 (stone, solid) and 寉 (phonetic component, representing "kaku"). Together, they convey the idea of something firm and solid — hence, “certain” or “confirmed.”

もう一度いちど 確認かくにんしてください。
Please check (confirm) one more time.

この情報じょうほうは 確実かくじつですか？
Is this information certain?

カク (kaku) is the on-yomi and is common in compound words. たしか and たしかめる are the kun-yomi and are often used in everyday expressions like 確かに (certainly) and 確かめる (to verify).