According to
http://en.wikipedia.org/wiki/Network_topology
A network topology is the layout or map of the pieces of a network. The topologies ring, bus, & star are be physical network topologies, as in real physical objects that constrained by real world physical limits. So the topologies are real and they make a picture. Star looks like a star. Ring looks like a ring. Bus is usually pictured as a straight line.
The bus, ring and star are physical network topologies.
See the following links for descriptions & pictures of the topologies.
http://compnetworking.about.com/od/networkdesign/a/topologies.htm
http://computer.howstuffworks.com/lan-switch2.htm
http://fcit.usf.edu/network/chap5/chap5.htm
Pay attention to picture only:
http://www.britannica.com/eb/art/print?id=68195
Advantages and disadvantages of Bus to be found here:
http://en.wikipedia.org/wiki/Bus_network
When thinking of a bus network, picture it as a fat line, like a real world school bus, and then picture all the students (nodes on a network) sitting in the bus (directly attached to the bus). The bus network topology is not as common as it was 10 years ago. Thinnet and thicknet were the common used networks 10+ years ago and are examples of bus networking. Today, thinnet and thicknet have been obsoleted by various flavors of Ethernet (10 Mbit, 100Mbit, 1000Mbit).
Picture of Bus Network:
http://au.geocities.com/lev_lafayette/manual/bus.gif
http://www.edrawsoft.com/images/network/Bus-Network-Topology.png
Advantages and disadvantages of Ring to be found here
http://en.wikipedia.org/wiki/Ring_network
"A ring network is a network topology in which each node connects to exactly two other nodes, forming a circular pathway for signals: a ring. Data travels from node to node, with each node handling every packet."
Ring looks like a ring, each thing is connected via cable to another thing in something like a circle. Typically used in FDDi fiber optic networks.
Note: Token Ring network is not is most cases used in a a Ring Topology. Instead Toekn Ring is usually used ine a Star Topology.
Advantages and disadvantages of star to be found here
http://en.wikipedia.org/wiki/Star_network
"Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central switch, hub or computer, which acts as a conduit to transmit messages. "
Star network is best understood as a central point of contact (the hub or switch) and the nodes radiate out from it like spokes on a bicycle wheel. Our common everyday wired ethernet networks (10/100/1000 Mbit/sec) use a star topology.
Many of the following links use plenty of technical jargon. Given that this assignment is asking for your own words, you should be able to go through the technical jargon and filter it out and write it up in your own way.
Contact me or wolf via e-m*** if you need someone to proofread it.
My biggest problem is I understand to a point what I am reading but not enough to form and write an answer in my own words..so in short HELP!!!