These terms are sometimes used interchangeably, but there are differences between each which it is useful to remember.
A Port is generally a description of a place on the coast which has facilities for boats or ships to call into, and usually a village or town attached. Normally these places developed because the natural features at that particular part of the coastline (a break in the high cliffs, an area of deepwater where the coast is rocky etc.). Because a port is a description of a type of function, ports can look very different from one another and a port may contain all of the things listed below (wharfs, quays, piers etc.). Porto Cervo, in Italy, is a good example.