"apply for registration"是社麽意思?

剛讀了移民局官方網站,發現有這麽一段文字不是很懂,請高手賜教
All aliens in the United States who are required to be registered under the law (INA § 262 and 261) must keep the USCIS informed of their changes of address.

Sec. 262. [8 U.S.C. 1302]

(a) It shall be the duty of every alien now or hereafter in the United States, who (1) is fourteen years of age or older, (2) has not been registered and fingerprinted under section 221(b) of this Act or section 30 or 31 of the Alien Registration Act, 1940, and (3) remains in the United States for thirty days or longer, to apply for registration and to be fingerprinted before the expiration of such thirty days.

(b) It shall be the duty of every parent or legal guardian of any alien now or hereafter in the United States, who (1) is less than fourteen years of age, (2) has not been registered under section 221(b) of this Act or section 30 or 31 of the Alien Registration Act, 1940, and (3) remains in the United States for thirty days or longer, to apply for the registration of such alien before the expiration of such thirty days. Whenever any alien attains his fourteenth birthday in the United States he shall, within thirty days thereafter, apply in person for registration and to be fingerprinted.

(c) The Attorney General may, in his discretion and on the basis of reciprocity pursuant to such regulations as he may prescribe, waive the requirement of fingerprinting specified in subsections (a) and (b) in the case of any nonimmigrant.

1. "to apply for registration" 請問社麽是"registration",我都不知道自己做了沒有,也沒人通知,是不是當初在學校F1時就做了(現在是H1)?若是,都忘了是則樣的了?
2."to be fingerprinted before the expiration of such thirty days." 請問每個人都要去按指紋嗎,不管申請還是不申請綠卡?

謝過了