Create the bitmap and set the pixels. Then set the PictureBox's Image property equal to the Bitmap.

' Get the drawing area size.
wid = PictureBox1.ClientRectangle.Width
hgt = PictureBox1.ClientRectangle.Height

' Allocate the form's drawing buffer.
bm = New Bitmap(wid, hgt)

' Get a new color.
If m_UseRed Then
    clr = Color.Blue
Else
    clr = Color.Red
End If
m_UseRed = Not m_UseRed

' Draw the picture's pixels.
For Y = 1 To hgt - 1
    For X = 1 To wid - 1
        If (X \ 20) Mod 2 = (Y \ 20) Mod 2 Then
            bm.SetPixel(X, Y, Color.Black)
        Else
            bm.SetPixel(X, Y, clr)
        End If
    Next X
Next Y

' Display the image.
PictureBox1.Image = bm

• Fill a large area one pixel at a time using PSet (slowest)
• Fill a large area one pixel at a time using a Bitmap object in VB.NET (faster)
• Fill a large area one pixel at a time using SetDIBits (even faster)
• Fill a large area one pixel at a time using SetBitmapBits (fastest)