Was wondering if anyone could me or give me some pointers/help

So I am about to carry out the pendulum experiment, changing the length of the string.

So I need to plot the graph of T^2 against L including the error bars. Now if I state that each period has an error of +-0.2 and the length is +-0.1cm.. are those the errors for the error bar for each length?

Now it then says I have to draw a maximum and minimum line of best fit through the error bars. I have just looked online and it says about Joining the smallest on one to the top of the other and vice versa. Is this how to draw maximum and medium lines?

Find the gradient of the lines. The gradient should be equal to 4π2/g. I am guessing that it is just a normal gradient equation for the both lines. But the equal to 4π2/g is getting me slightly confused? How do I use the gradient to find g?