To sort information means to arrange it in a chosen order. A list of names might be sorted alphabetically, or a set of prices might be sorted from low to high.
Imagine spreading several cards across a table and lining them up from earliest date to latest date. Sorting helps people find a particular item or compare the items more easily.
The order needs a clear rule. If a page sorts by date, for example, it should be clear whether the newest or oldest item comes first.