Custom report templates are XSLT documents that transform the generated XML data into some other format. Generally you will want to transform the data into some type of HTML, XML or CSV data, but you could theoretically transform the data into any textual format.
To start creating templates, you will need to download the sample XML data or use your own data by going to the Custom Reports tab and selection Export to Raw XML from the export dropdown. You can then save your own raw XML data to test with.
Depending on the type of report you are trying to create, you may find one of the sample templates useful as a starting point.
Note: At the top of your XSLT document, you should specify the type of file you are creating. This is done by specifying a special variable called "exportType".
By default, it is assumed that you are returning HTML but you could set this variable to XML or CSV if that is what you are generating.
Whether you create your own or use the sample one, you will need a way to test the transformation. While we suggest using a tool such as XMLSpy, there are online tools for testing XSL transformations as well.