When 自然 used as a noun it represents the nature of the world but we do not use it on human being. But this word can be used as a sort adj or adv to describe the behavior of humans. you can use it to describe your attitude or mood (it can indicate you are peaceful or relx or not nervous) or you can use it to describe your actions which can mean that you are not nervous when you doing something ( usually you can use it to describe the actor giving performance)

“自然” can be used as a noun, an adj. or an adv. in different contexts. So it is equal to nature, natural, or naturally in English. I'd like to paraphrase its usage in following expressions. 1. 我们要亲近（大）自然。= we should be close to nature. 2. 他的表演很自然。= He performs very naturally. 3. 他神态自然。= He is at ease. 4. 自然资源= natural resources 5. 自然规律= laws of nature 6. 自然现象= natural phenomena Hopefully the above can help you understand better about 自然。

我們說"他的腔調不自然". "他的頭髮是自然鬈".或者 "他天生一副好嗓子". "他天生鬈髮" (以上有關人物的描述) "天然氣(天然瓦斯)". "天然的洗碗精最好". "天然琥珀很稀有". "自然環境". "自然發展". "天然環境". "天然形成". "朝夕相處之下. 他二人自然而然地成了好朋友"(指情境) (以上對於人物以外的描述)

自然 means nature, right! 它也是一种感觉的形容词 a kind of feeling,for example“relaxed”or“comfortable”

Yes， besides the meaning of nature, it also means not acting with affectations, not be coy when it is used to describe peoples and their actions. Hope this helps.