trying to understand a credit

i was on youtube all last night trying to understand all this . APR , closing date . and due date . trying to choose which credit card company is i should go with because because i know they say if the apr fee is high (whats considered high?) then dont get it . and i know if i apply for a credit card with NO credit and i dont get approved it can also mess up my credit . i just need help , this shit is so confusing . amd also CAN I STILL APPLY EVEN IF I AINT START MY JOB YET. I START IN ABOUT 1 WEEK