(1)enter 后面接具体空间位置场所，不需要加介词into。因为enter +地点名词=go into +地点名词

He entered the room briskly and stood near the door. 

他轻快地走进屋里，站在门边。

Before entering the bathroom, he emptied his dirty laundry into the hamper. 

进浴室前，他把脏衣服全都放进洗衣筐里。

(2)enter into +名词+with sb加入（讨论）;订立（协议）;开始（关系）

I have not entered into any financial agreements with them.  

我还没有和他们订立任何财务协定。

We entered into meaningful discussions with them weeks ago.

几周前，我们和他们进行了意义深远的讨论。

(3)enter into +名词成为…的一部分；成为…的一个因素；构成

There were also other factors that entered into the orchestration.  

管弦乐编曲还要考虑其他因素。