Principiante / aprendiz / iniciante
Abecedarian (estar no beabá?) = One who teaches or studies the alphabet. One who is just learning; a beginner.
Beginner = One that begins. One who is just starting to learn or do something; a novice.
Freshman (calouro) = A student in the first-year class of a high school, college, or university. A beginner; a novice.
Fledgling (inexperiente, frangote) = A young bird that has recently acquired its flight feathers. A young or inexperienced person.
Greenhorn (novato, simplório, ingênuo) = An inexperienced or immature person, especially one who is easily deceived. A newcomer, especially one who is unfamiliar with the ways of a place or group.
Initiate = One who is being or has been initiated. One who has been introduced to or has attained knowledge in a particular field.
Neophite= A recent convert to a belief; a proselyte. A beginner or novice: a neophyte at politics. Roman Catholic Church. A newly ordained priest. A novice of a religious order or congregation.
Newbie (inexperiente?) = One that is new to something, especially a novice at using computer technology or the Internet.
Newcomer (recém-chegado) = One who has only recently arrived.
Novice = A person new to a field or activity; a beginner. A person who has entered a religious order but has not yet taken final vows. Also called novitiate.
Rookie (slang/gíria) (recruta/novato) = A beginner; one who is new to a profession or field. “Rookie” is a slang. Example:1) Brazil played like a bunch of rookies against Equador last Saturday, lets hope they play better on Wednesday!!! 2) It's not easy being a rookie police officer. Etymology: This word is derived from 'recruit', a new member of an army.
Tenderfoot (novato) = A newcomer not yet hardened to rough outdoor life; a greenhorn. An inexperienced person; a novice. often Tenderfoot A Boy Scout of the lowest rank.
Tyro (principiante) = A beginner in learning something. Ex.: He was a sensitive, fine soul alert to the pleasures of being green, a tyro, an amateur, unwilling to close his mind before it had been tempted
Sources: Knights English / Answers.com