One of the challenges faced by an entrepreneur when setting up a business in Poland is registration with the Social Insurance Institution (ZUS). Reporting to health and social insurances may be a challenge. Especially when a foreign employer or shareholders must be reported. 
To learn the basics of registering a company, partnerships or a sole trader ship with the Social Insurance Institution, one has to become acquainted with the following topics: 

• Partnerships registration with ZUS 
• Reporting shareholders to insurance 
• Registration of a sole trader ship with ZUS 
• Reporting a foreign employer to the social and health insurances 

When discussing this topic, it is also worth mentioning that there are situations when you do not have to pay ZUS contributions. These are some kind of reliefs, such as "Ulga na start" or a possibility of running a business without registering it. 

All the possibilities and differences in registering with the Social Insurance Institution depending on the type of business activity, have been discussed in the following article: 
https://pl.vgd.eu/en/newsroom/registration-for-the-social-and-health-insurance-in-poland/