Timeline reports are useful for visualising data such as spend over time. 

You can split your report into the required level of detail by adding / removing dimensions in the report builder in the normal way.

You need to select a minimum of 3 dimensions and 1 metric for a timeline report and the final dimension defined in the report builder should be a time dimension.

Example:

The first dimension - in this example 'Market' - will be the first column in the report: 

The second dimension will define the level of detail at which information is plotted in the main area of the timeline report.  In this case our 2nd dimension is 'Channel' so the timeline plot shows the performance for your chosen metric at the Channel level. The name of the Channel will be displayed on the plot.

If you want to plot a greater level of detail in the timeline view, with more detailed breakdown of the data, you can add additional dimensions in the report builder.