A trade licence / business licence (živnostenský list) allows its holder to work in the CR on a self-employed basis i.e. as an independent contractor/freelance worker without a working contract (English): https://www.mpo.cz/en/business/licensed-trades/guide-to-licensed-trades/
STEP 2: Select trades that are relevant for focus of your work.
STEP 3: Prepare the following documents: passport, confirmation of a business seat, a criminal record check. Registration fee is 1 000 CZK. A trade licence is usually issued within 15 days (the authority has 30 days).
STEP 4: Register for taxes, social security and for health insurance.
At all Trade License Office (Živnostenský úřad) (English): http://www.rzp.cz/eng/index.html.
Who is eligible: You must be at least 18 years, to be legally able to enter into a contract.