Excel doesn't have a separate Gantt chart type. You build one from a stacked bar chart. Each task needs a start value and a duration. The first series positions the bar at the task's start, and the second series shows how long the task takes.
Select the task, start, and duration columns, then insert a Stacked Bar chart. In Format Selection, set the Start series to No Fill. Its width still pushes the duration bar to the right, but the reader sees only the duration. A clustered bar chart would put the two series beside each other and lose that offset.
Reverse the category order so the first task is at the top. Remove the legend when the only visible series is clearly the duration. A zero-duration task has no visible width, while a task beginning at zero starts at the origin. Keep the source linked to the task list so moving a start date or offset moves the corresponding bar.