Being under the age of 18 does not change whether you require a visa, but there are differences in visiting the UK. You can find out whether you need a visa here, but need the following info:
If you do need a visa you can normally get it online or in person, but find out the process for the country where you live. Applying for a visa also included giving biometric information, where your fingerprints and photo is taken-this is to stop someone stealing your identity.
Visas cost £65 and take about 4 weeks to come through, but make sure you leave lots of time, and that you buy your travel tickets once your visa arrives.
As someone under the age of 18 the UK government need the following for you to travel
As a young person you also have the choice of 2 visas which are
You can find out more about visas on the Government visa website, and specifically for family members including young people here.
If you are able to get your visa online, apply here