Integrated circuits are descendants of vacuum tubes where the numbering was in a circular pattern. Thus, the Basic Stamp terminal numbering is in a counter clock wise manner. However, on the 10-pin header, the terminals are assigned much as we read. An arrow on the header identifies terminal 1. Note that ground is connected to terminals 4 and 23 of the Basic Stamp and terminal 5 of the 10-pin header.
Black wire is suggested.
Leave terminal 21 unconnected. Note that in addition to ground, there are three leads from the header to the Stamp and a strap between terminals 6 and 7 on the header. Any color of wire other than red and black is suggested. You may also wish to connect one side of a black lead to terminal 22 as well. Leave the other side unconnected for the moment.