I'm curious about teeth whitening... I want to know about its effects and side effects.

My teeth are somewhat yellow, so I've become interested in teeth whitening lately...

So I need to search the internet and do that, but I'm too lazy, so I just think about it but can't put it into practice.

It makes me nervous every time I smile... and also when I talk...ㅠㅠ
I recently managed to get toothpaste that is said to be good for teeth whitening...

Is teeth whitening at the dentist effective?

Some people say it's not good... Are there any side effects?

How much does it cost?