The Simulator function conducts simulations similar to conjoint-style market simulations. You select which items are to be made available to respondents (as if they were in competition with one another within a marketplace). The percent of respondents projected to "choose" each item as "best in market" is computed, according to either the first choice or the Share of Preference (logit) rules.
First Choice: Each respondent "casts a vote" for the item that has the highest score within the items included in the simulation set. In the case of a tie (a rare occurrence), tied items share (divide) the vote. The interpretation is simple: "Considering only these x items, what percent of the respondents think each is best?"
Share of Preference (Logit): Respondents are allowed to split their votes across the items included in the simulation set. The probability that an item is selected is equal to the antilog of the item's raw score divided by the summation of the antilogs of the raw scores for all items in the set.
You will generally find the projected "shares of choice" a bit more extreme for the First Choice than the Share of Preference (logit) rule. You will also find that the logit rule's estimates are more precise (smaller standard errors), because more information is gleaned from each respondent. But, the First Choice rule is easier to describe to others.
The standard errors can be used to compute a 95% confidence interval for the estimated share of choice, by taking the estimated share of choice +/- 1.96 times the standard error.