Where do you even start?
If you live on the budget/finance side of the house, you can easily get started by looking at your budget lines and starting to categorize them via the cost pools and potentially towers. You will quickly learn if perhaps you need to adjust your budget to be more granular to get to the tower level. From this simple exercise you can start showing your data in a different way (even visually via pie charts, bar graphs, etc) to your leadership and stakeholders and beginning to have value adding TBM conversations.
If it's starting with Apptio and the tool then I would start by doing the CT foundation training as it gives you a good understanding of the tool and some of the TBM principles.
In general Community is where I learnt the most and is where I come back to time and time again
Retrieving data ...