employer will boost my income based on how I perform during the 3 months but he also told me this place mainly to learn gain experience and not to earn much money.

This reads like a red flag tbh... Sounds like an excuse to underpay you. Make sure you have a list of what you should learn by a certain time frame, to prevent yourself from being exploited.

to your last question: if you can crack the code please let me know.

in general, my advice:

• pay close attention to the unspoken norms and culture of the office.
• better to be slightly overdressed (formal wear) on your first couple of days then otherwise.
• Don't mind all the seniors making sarcastic comments about the job, though pay attention to what exactly they're being sarcastic about.
• you don't have to be excessively friendly, but be open. are you assigned a work buddy for the week? if not just be a bit of a busybody and ask if you can join people for lunch (depends on your level of comfort of course), or at least follow people's lead on where they're going. this week is not for you to do your own unique spin yet.
• HR likely will bring you around to the office, but sometimes ppl will not be at their desk when they do bring you around - so here's a thing I will tell you you must do that a lot of juniors too segan to do: if you're at the office and you terserempak someone you weren't introduced yet, for the love of any deity you believe in, go and introduce yourself.
• (this will help you down the line especially when there's a team meeting etc - if they at least remember your face you might have better chances to be included in random stuff that might help you learn)
• if you're quite don't know what to do in the first week, show initiative and ask for something to do. You don't have to do it fast, but you just don't want to let ppl wonder, so exactly what is newbie doing rn? helps to save you from being comandeered for random ass duties too
• the janitorial/cleaning staff is your friend. find out their names or at least don't you ever forget to thank them if they're cleaning your workstation or say hi when passing by.
• receptionist and admin staff is also your other new friends.
• you don't have to join every chatting session but keep your ears open
• one of these days, for breakfast, bring something or a snack for the day. don't be weird and make sure each terminal gets a piece of that food, but let ppl know you brought something and it's at the pantry.