Hello;
To answer your question right away, any skill chosen by the player must be simple. This is stated in the “Starting Skills at Character Generation” section, third paragraph. (Page 35.) “Any starting skills after the initial 2 can be skills of the player’s choosing, as long as the rank of the chosen skill is Simple.”
As you have noticed the first two skills at character creation must be rolled for, but the third, fourth or fifth maybe chosen if desired. If chosen, the player may choose from any available skill, not just those on the chart listed in the “Starting Skills Determination” table. That chart identifier is only if you choose to roll for the skill, which gives you a chance of starting with a skill higher than Simple.
Hope this answers your question and thank you for posting.