the hello world example:
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root[0] TPaveLabel hello(0.2,0.4,0.8,0.6,"Hello World");
root[1] hello.Draw();

- "hello" is an object of the class "TPaveLabel"
- "0.2,0.4,0.8,0.6" are the lower and upper coordinates of the Pave (the range is from 0 to 1)
- the second command will draw this object and will automatically create a graphics canvas