Once you've opened the data, there are two approaches you can take.
The first: understand what the data means conceptually, then think about what you could calculate from it. The second: look purely at the structure — which columns could be grouped together, which columns could link tables — and work from there, without worrying about meaning yet.
Neither approach is wrong.
For example, even if you have no idea what this spreadsheet is about, you can already see: the left table scrolls way do