I would like to learn how to reproduce the famous sinus scroller text effect, but i can't make it to work.

Can someone explain the idea behind this ? I don't want the code (i want to find it myself), i just want to understand how to approach this.

I've created a table with a cell for each letter of my text, now i need to print and move each later to the left in a sinus pattern, but i can't figured out :

cls()
table={1,2,3,4,5,6}
x=127

function _update()
end

function _draw()

for i=1,6 do
print(table[i],127-i*10,cos(i*3/12)*20+60)
end

end

With this i have a sinus with my text, but it's not moving in real time, and it's in reverse mode. At some point i need to erase each letter from their previous position ? How to erase only one printed letter ? Print the same letter at the same position with transparent color ? Maybe sprite are better for this because they are easiest to move ?