Karac Cano
Professional procastenator
In the United States, if you want to find out if you need to file your taxes you can go to this site: http://www.irs.gov/uac/Do-I-Need-to-File-a-Tax-Return?
If you do have to file, yes you technically have to report it. But, if AdSense or your network doesn't report your earnings on a 1099 the IRS doesn't know about it. Most places wont even generate a 1099 unless it's over $10. It's up to you how you want to handle that.
If you do report it, you can offset your tax liability by deducting expenses and other stuff on a schedule A (provided you're treating this as a hobby for tax purposes and you itemize). Unless you own your own house, you're likely taking the standard deduction anyway. And even if you itemize, you can only claim the amount above 2% of your AGI. As a hobby, your deduction can't exceed gross income from YouTube. The IRS website has plenty of information on this. See Pub 535 for more info.
True, also if you receive most of your income from adsense aka your career you will have to file a w9 form if you live in america or proof of independent business cause youtube sees you as a indie contracter then a worker so you have to go through some different forms blah blah blah. Only if you are receiving most of your earnings through youtube and not as a hobby.