The first - and in most cases the only - step is to download all your transactions from Math Wallet and upload them into Koinly. There are a few ways you can do this:
If you want to import CSV files, you must make sure to import your deposits/withdrawals and trades for ALL years - not just the current one!
That's pretty much it. Don't forget to tag your airdrops/forks so they show up as Income on your generated cryptocurrency tax forms!