The current service returns a ranked (with scores) list of up to 200 entities. You can specify a type in your query or filter the results to select types of interest (e.g., Person, Place or Organization). The top result for 'apple' is the Corporation 'Apple, Inc.' and #2 is Thing 'apple' (a fruit). The score is probably based on a graph popularity metric (e.g., number of inlinks) possibly augmented by pagerank. Interestingly, the knowledge graph ID is the same as the Freebase MID and the results for the KG search for 'apple' appear to be a subset of a similar Freebase search and also in the same order.