Im assuming you mean programming languages. At the least youre going to need to know javascript and html/css. on top of javascript you will need to know some how to use frameworks, build servers, deploy apps, testing, etc
you can finish a course in 3 months but its tough for most people to get a job right after especially if you didnt go to a bootcamp and you taught yourself.
you will need to have a decent portfolio of work to show employers and also be pretty proficient in using various tools.
you can start applying for jobs when ever you want but you might have a hard time getting people to notice you with only 3 months of experience
on a more positive note check out this post