Tone curve Lightroom Mobile

[MatteManz]

Might be a stupid question but I'm really new to this world and I don't get what's the fourth type of tone curve besides the general and the RGB in Lightroom Mobile. 

Anyone who can help? 

[Rob_Cullen]

The left-most button is a "Tone" curve- you can only 'push' the curve within the lighter shaded area on the graph and it works similar to adjusting tone sliders.

The Grey circle button selects a "Point" curve- you can place several points on the line to move as you please. The grey circle point curve adjusts all RGB channels together.

The colored circle buttons are also "Point" curve adjustments but for each specific RGB channel.