Tax // Trademark

Hi,

Im 17 and im starting my own business up. I am worried about two things that hopefully the member here can help me with:

1) Tax, What are the rules on having to pay tax if you are earning money in this way by web design or coding, Do i have to pay and how and when?

2) Trademark, Is it necessary to become a tm? I have heard from some people you are aloud to trade under a name thats not already trademarked, however if someone trademarks the name, its tough to you really, As you havent registered it.
can i do this and not register it?

Also, How much would it cost and what would it involve to register it?

Thanks for your help,

Steven
Klear Concepts