Hi felipehbatista86,
If you have a business as a self-employed individual, you can track your transactions in QBSE, so at the end of the year, it can estimate your taxes. If you're also employed as a courier, you can enter your Estimated Employment Income on your Tax Profile.
If you're sub-contracting as a courier, you can still track your transactions like having a sole business.
In regard to determining if you are self-employed or not, you may check out the guidelines from the UK government's website. Articles below.
Intuit articles:
Please let me know if you have other questions in mind. Have a good day!