CloudWatch console home page by default shows you metrics about AWS services you currently use. Additionally you can create custom dashboards to display metrics about your applications and AWS resources, and display custom collections of metrics that you choose. CloudWatch gives you complete visibility into resource utilization, application performance, and operational health.

More information on CloudWatch can be found here AWS CloudWatch User Guide

Using CloudWatch metrics, you can create alarms to send alerts or automatically make changes to your resources when a breach condition is triggered. For example, say you are running an application on EC2 instances and you want to monitor the CPU usage and other resources consumption of your EC2 instances and if there is an increased load, then use that data to determine whether you should launch additional instances to handle increased load. You can also use this data to shut down EC2 instances when they are under utilized due to no work load.

CloudWatch console CloudWatch overview screen
custom dashboard

In addition to automatic dashboards that AWS creates, you can also create custom dashboards for your needs.

, CloudWatch custom dashboard