Change the date in the cell shown.
Text and background are the same color, so you can't see the date. But it's there!
Enter dates; colors & shading should update automatically. There's no functionality for complicated gantt-style dependencies, but you can use formulas here to encode simple dependencies.
Go to the "Color Key" tab to change what labels you use in column H.
Change the label for each color.
The only way to change the colors is by updating the conditional formatting everywhere.
Copy-paste your dates into different tabs to see the schedule on different time scales.