Matter
Item, Subject
noun
You know 事 means "occurrence," but it can also mean "matter." So a matter paragraph shows the matters, items, or subjects that make up a larger issue or discussion at hand.
事項 is a formal word usually seen at the end of another phrase that specifies what matters or items are being referred to, like 注意事項 (matters to be noted) or 協議事項 (items for discussion).
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
用紙に必要事項を記載のうえ、郵送をお願い致します。
Could you fill out the form and mail it to us, please?