All modal verbs are auxiliary verbs, which means they can only be used with a main verb. Modal verbs cannot be a main verb. They are used to express ideas such as possibility, prediction, speculation, deduction and necessity.
British vs. American English: 63 Differences
Learn one Kanji a day with infographic: 弁 (ben) - http://japanesetest4you.com/learn-one-kanji-a-day-with-infographic-%e5%bc%81-ben/