Student credit cards & bad credit

Looking for 1-2 sentence responses to the following (brevity is encouraged/appreciated!): What’s one of the first steps a student can take to build credit? How would you explain a variable APR to someone who has never used a credit card? What makes a student credit card different from other credit cards? Requirements: Professional expertise related to credit advising, credit cards for students, or personal finance matters for college students – your title should clearly indicate your professional authority related to these topics.