In what ways does a Gantt chart and network diagram aid in the completion of a project ? What information does it provide and how is that information used ?
These are very broad subjects in Project Management, but as a short introduction it goes like this:
Gantt charts are a tool for scheduling. They show how activities relate to each other over time. You list all the activities as horizontal bars where the size and position of the bar within the chart show when each activity starts and ends, how long it lasts, where there is an overlap in activities, who does the work for each activity, etc. Laying out all the activities in this way shows you how you will do the work from start to finish of your project. It allows you to visualize and organize the work so that you perform those activities in the proper order. It also allows you to track progress as tools exist that can combine the Gantt chart you laid out, with actual work performed on the activities and see if you are on track or not, and if you need to adjust what you are doing.
Another way to visualize the activities and how they relate to each other is the network diagram. The Gantt chart has a focus on schedule and timelines, while a network diagram helps with planning by identifing dependencies between the activities, determining the sequence of the activities, finding the activities on the critical path (i.e. the activities that can't be delayed without delaying the whole project), how much slack you have in performing other activities that are not on the critical path before they start delaying your project or other activities (known as "float"), etc.
You usually use a network diagram to see the relations between activities, their dependencies and impact on each other, and then you use that information to build a Gantt chart to lay all of these activities against a time horizon and build a schedule of how you will perform the work.
See the following page for some differences: Difference between Gantt Chart and Network Diagram.