Can someone explain this function?

I am currently trying to use the boundedline function to plots 95% confidence intervals (seen below). I have sucessfully managed to plot something but I use a random number for 'b'. Can someone explain what b means here? I don't understand what is written in the help manual.

boundedline Plot a line with shaded error/confidence bounds

[hl, hp] = boundedline(x, y, b)
[hl, hp] = boundedline(x, y, b, linespec)
[hl, hp] = boundedline(x1, y1, b1, linespec1,  x2, y2, b2, linespec2)
[hl, hp] = boundedline(..., 'alpha')
[hl, hp] = boundedline(..., ax)
[hl, hp] = boundedline(..., 'transparency', trans)
[hl, hp] = boundedline(..., 'orientation', orient)
[hl, hp] = boundedline(..., 'cmap', cmap)

Input variables:

    x, y:       x and y values, either vectors of the same length, matrices
                of the same size, or vector/matrix pair where the row or
                column size of the array matches the length of the vector
                (same requirements as for plot function).

    b:          npoint x nside x nline array.  Distance from line to
                boundary, for each point along the line (dimension 1), for
                each side of the line (lower/upper or left/right, depending
                on orientation) (dimension 2), and for each plotted line
                described by the preceding x-y values (dimension 3).  If
                size(b,1) == 1, the bounds will be the same for all points
                along the line.  If size(b,2) == 1, the bounds will be
                symmetrical on both sides of the lines.  If size(b,3) == 1,
                the same bounds will be applied to all lines described by
                the preceding x-y arrays (only applicable when either x or
                y is an array).  Bounds cannot include Inf, -Inf, or NaN,

    linespec:   line specification that determines line type, marker
                symbol, and color of the plotted lines for the preceding
                x-y values.

    'alpha':    if included, the bounded area will be rendered with a
                partially-transparent patch the same color as the
                corresponding line(s).  If not included, the bounded area
                will be an opaque patch with a lighter shade of the
                corresponding line color.

    ax:         handle of axis where lines will be plotted.  If not
                included, the current axis will be used.

    transp:     Scalar between 0 and 1 indicating with the transparency or
                intensity of color of the bounded area patch. Default is
                0.2.

    orient:     'vert': add bounds in vertical (y) direction (default)
                'horiz': add bounds in horizontal (x) direction 

    cmap:       n x 3 colormap array.  If included, lines will be colored
                (in order of plotting) according to this colormap,
                overriding any linespec or default colors.

I have 2 time series, time and data (1x663, 1x663) which I am using for x & y.

thanks, Michael