I'm new to the game. If I get a job I don't really like (but have to take it to not lose my OPT) and keep looking for a better place, can I quit the job at any time ? Are there any legal obligations like contract and stuff (like in Europe) ?
Assuming the US you can quit and walk out. The company, unless there are unusual terms in the contract, can't sue you to continue working. That said, you may be obligated to pay back a relocation or signing bonus.
Don't expect your coworkers, manager, or others to think fondly of you and support you with references or want to work with you again if you provide zero notice. Two weeks is considered reasonable and professional.
Due to at-will, once an employee gives notice, the Employer can terminate immediately or let you continue until your resignation date. I have seen employers terminate people : -the end of the same business day that they gave notice; -the first Friday after the business day they gave notice; -a couple business days before their final scheduled day. This was in the private and government sectors and people were given between 1 hr and 1 day’s notice when this happened. All were at toxic work environments.
You can, but OPT has a limit on how many days of unemployment you are allowed to accumulate.
There is no unemployment eligibility for those who are jobless because they resigned.
That's not what I'm talking about, OPT has limit on how many days you can be on it without having a job
You can always quit at any time, but you need to think of the ramifications of doing so. It's always harder to find a job when you aren't working and people do talk. If you leave under bad circumstances, you risk being blacklisted or worse. Keep that in mind before leaving any job.
Yes but exceptions https://www.betterteam.com/at-will-employment The article is the employer perspective but generally applies to the employee as well.