In the case of a towered airport it will be broadcast over the ATIS, Automatic Terminal Information Service, as a letter coded collection of information. This will include the time of the observation/recording, the weather, general conditions and operating notes for the days operations. This usually can be received a fair distance from the airport allowing you to plan your approach whether visual or instrument. Not all towered airports use an ATIS and they use a method similar to below.
For a non towered airport the weather broadcasting service, whether AWOS, Automatic Weather Observation System or ASOS, Automatic Surface Observation System will broadcast the current conditions typically every minute depending on human added notes appended to the recording. Using the current conditions you determine the best runway to use based on the winds or other factors such as sun position if the wind is calm or obstacles/terrain requiring the use of one runway or the other.
For airports without weather observation other than a windsock, tetrahedron or flag in the breeze you use those as a method of determining which way to land. Some places have preferred calm wind runways for noise abatement or other reasons which depending on how thorough the airport manager is can be either in the A/FD or hidden someone in local lore.
