Something that's cheery makes you feel happy. A cheery summer day is sunny and bright.
It's always fun to spend time with a cheery friend, one who is positive and happy, or to participate in some cheery activity, like watching a funny movie or having a picnic. Cheery things do exactly what they sound like — they cheer you up. You can also use cheerful to mean the same thing, and both words are rooted in cheer, from the Anglo-French chere, "the face," with its Greek root kara, "head."