Laying down memories
You go to a party: you listen to music, try the food, see your friends. These experiences trigger activity in several areas of your brain: those dealing with sound, taste and sight. You now have a unique memory of the event. A month after the party, you might bump into someone you met there. Seeing them might trigger other memories of the party - the music, the food, that rather attractive person... Once you have remembered one part of a memory, it is easier to retrieve the connected bits.