语法错误主要有以下几点：
1.Nature just likes an old man,it can tell you something about life and what you are doing.
应该为：Nature is just like an old man,which can tell you something about life and what you are doing.
你原句中的like用作动词,有第三人称单数.但like用作动词时意思为“喜欢”.但明显你所要表达的意思是“像”,但like只有作为介词的时候才有“像”的意思.因此要把like改为介词形式的,前面加be.
然后it要改为which.因为你前面用的是逗号,一个句子没完的.所以后面应改为一个从句吧,用which引导.
2.I like listening the songs of birds,and I like smiling to each flower
listening后面要加to.listen to sth
3.People when see that,always laugh.
应改为when people see that,they always laugh
或改为：when seeing that,they always laugh 也可以
4.I JUST WANT TO BE WHICH I WANNA BE.
which 改为 what
be 后面的不是定从是表语从句,不应该用which 引导的.what引导表语从句.
LZ写得不错的～只是有点语法错误.加油!