The numbers in the tables represent megabytes, and approximately 1000 megabytes = 1 gigabyte.
You are provided with two different disk space / bandwidth measurements. The first table lists usage by domain and the second table lists total usage. Total usage is generally higher than domain usage because total usage statistics include factors that are separate from your domain, such as MySQL databases and control panel use. It is possible to host several domains on one account, so separating domain and total usage is necessary.
Note: DirectAdmin uses total usage (not domain usage) to determine when quotas have been exceeded.