There are a number of ways to display the contents of a table, all from the Database Explorer window:
click on the table, then either:
right-click and select Display
click on the Table > Display Table menu option
right click and select View > Contents (first 30 rows). This will display a sample of the table (the first 30 rows) in the right-hand grid. Tables will be displayed as you select them by clicking on them (or using the keyboard up and down keys to scroll).
click on the Run SQL menu option / icon to bring up the Run SQL window. To display the table, click on Run or hit F5. You can use this window to build more complex queries on the table.
click on Table > Search Table (or the search table icon) will show you the Search Table window. This allows you to select which rows in the table you wish to display. Clicking on OK will display the table.
Once you do any of these the contents will be displayed in the Data Display window.
Not all the rows in the table will be displayed. By default only the first 1000 rows will be shown. This default can be changed with Options > Display Limits. If you are running the Evaluation version of Advanced Query Tool you will only be shown the first 50 rows, and you will not be able to increase this.
For very long columns, by default only the first 200 bytes of the column will displayed. This default can be changed with Options > Display Limits.