The default sort for search results is Sort by Relevance, but you can select a different option using the sort menu at the top of the search results screen.
There is a limit, though – results will not be sorted if there are greater than 10,000 results. The number of results is indicated in the upper left of the search results screen.
In these examples, the results of a search for “dogs” cannot be sorted as there are more than 32,000 results, but a search for the more specific term “poodles” can be sorted as there are fewer than 10,000.