Is Anti-static bracelet necessary when building a new pc? 

Not really, hell even seasoned technicians don't wear them. They are a nice safety precaution, but a few things to consider would be to not work on carpet, touch bare metal on your case or power supply, and if you want a bit more peace of mind, a plugged in cheap psu nearby is easy and effective. 

are you telling me to touch bare metal or the power supply or not to? cause i have nzxt s340 and it is all metal case

Yes do touch bare metal, it will discharge on the case and not your sensitive hardware ie motherboard, ram, graphics card etc. 

Touching a painted surface won't help, total bare metal is what you need to touch.