How does it work?

The first - and in most cases the only - step is to download all your data from mxc and upload it into Koinly. There are a few ways you can do that:

MXC does not have an API so you will need to download your CSV files from their web interface and upload them into Koinly manually.
If the above method(s) are not possible for you, you can even add the transactions one by one through Koinly's web interface.

If you decide to use CSV files, you must make sure to import your deposits/withdrawals and trades for ALL previous years - not just the current one!

That's all you have to do. Don't forget to tag your airdrops/forks so they appear as Income on your final crypto tax reports!