Hello. As a beginner, how do i build an effective bankroll management? and why is it important?

It is important as if not managed correctly then you could lose your entire bankroll.

Bankroll management depends on a number of factors such as ability to reload, need to withdraw monthly for living costs (or not), poker variant and stakes being played etc.

If you are a begginner I would reccomend doing loads of study and saving up $5k from your job, so you can play a reasonable stake, at low stakes the rake is usaully higher so ideally start at a higher stake such as $50.

Typically it is reccomended to have 100BIs to minimise the risk or ruin/losing your roll, however at micro/low stakes and assuming you are playing NLH and not PLO then you should be fine on 30-50.

If you are a losing player, then no amount of bankroll will help.