• 悪夢あくむ — nightmare
• 夢中むちゅう — absorbed in; completely into something
• 夢想むそう — fantasy; daydream
• 夢見ゆめみ — dreaming; seeing a dream
• 夢幻むげん — dreamlike; illusory; fleeting
• 儚はかない夢ゆめ — fleeting dream; short-lived hope

The top component (艹) suggests growth and a net-like shape (罒), as if something drifting can be caught. Below, 冖 and 夕 represent night and sleep. Together, the kanji shows dreams — the visions we see at night and the hopes we try to catch and make come true.
Looking at the parts of a kanji like this helps you understand and remember its meaning. Try using the same idea with other characters, too.