Conditional formatting in Excel allows you to format a single cell or group of cells according to the data within them. In Excel you can chose to format a cell with highlights, data bars, colour scales or icons due to the rules that you can set; ultimately opening up endless data visualisation possibilities.
If you want to add a colour scale to a set of data you need to highlight the cells you want to apply it to.
Then click on the conditional formatting tab.
Then colour scales and select the colour scale you want.
You can also use data bars and icons.
You can also use conditional formatting to highlight duplicates.