turning a hand drawn picture into a vector

1) Scan the image into a bitmap. (file types that Inkscape recognizes include jpg, png, bmp, ...)
2) Import the bitmap into Inkscape (link or embed, it does not matter. But if you want to revisit and edit the image/trace at a later date it will have to be in exactly the same path on the computer if you 'link')
3) Call the "Path > Trace Bitmap" function [Shift + Alt + B]
4) Play with the perameters untill you get an acceptable result.
5) Remove the linked or embedded image
Learn more about Tracing bitmaps from the user guide: [ http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Trace.html ]

Lacking a scanner you can photograph the drawing, and import the image into Inkscape; perhaps after some image manipulation to make the tracing easier.