close

當動詞時是 “關、閉上”的意思

例如：close the door; close your eyes ...

當形容詞則為“親近、親密”的意思

例如：Tom and I were really close when we were in high school.

closed

主要就是形容 xx 是“關著的、封閉的、不在營業中”

例如：The library is closed on Sunday.

closely

主要是副詞功能，用來修飾動詞時表達“很接近地、緊密地、密切地”

例如：The crowd closely watch the players" every move as the clock winds down.

三個詞各有各的基本功能，必須根據語境試著去理解揣摩。上面提供的只是在常態下的用法。