Gantt charts are really just horizontal bar charts showing tasks. They're a quick way to see a graphical representation of upcoming work.
A Gantt Chart is a time scale with tasks plotted along the X axis. In other words, project task start and finish dates are plotted on a time graph with rectangular bars representing start and finish dates. Standard Time® includes a Gantt Chart with its project management features. Entering hours into the timesheet posts them to the tasks which show up in the Gantt Chart.
Henry Laurence Gantt invented the chart, which was later named after him sometime after 1910. Click here for the Henry Gantt Wiki article. Over a hundred years later, we still include a Gantt Chart in our product, for obvious reasons. This video and article explain how to read a Gantt Chart.
The main purpose of the Gantt Chart is to show task (start and finish date) relationships at a glance. All the tasks are plotted next to each other on a common time scale. This lets you scan the chart for relationships to one task to another. In other words, you can see when one task is about to end and another begin. You can also see duration relationships. I.e. how one task might be longer than another. This offers an easier absorbable snapshot view of task relationships; the brain processes graphics much easier than text.
Summary tasks are ones that include a list of actual working tasks under them. In other words, employees don't actually work on the summary tasks; they just represent an "umbrella" for the actual tasks under them. the Gantt Chart displays a rectangular bar with triangles at each end representing the earliest start and latest finish dates of the task under it.
Actual working tasks are represented by a simple rectangular task bar. A skinny bar inside the main task bar is the % Complete status. tasks that are over 100% have a % Complete bar that extends beyond the task bar.
Milestones are represented by a diamond symbol. Milestones are zero-duration tasks that represent project stopping points, usually for evaluation and reflection. They may also represent phase completions, deliverable dates, or ship dates. No actual work is done on a milestone, except for evaluating the project status at that point in time.
The video also shows how summary tasks can be collapsed and expanded to hide and show the tasks under them. This save task hierarchy is visible in the timesheet where employees can enter actual hours against each task.