Only if you are using personal data exclusively in the private or domestic sphere, you are not affected by the GDPR.
The GDPR applies to the processing of personal data wholly or partly by automated means and to the processing other than by automated means of personal data which form part of a filing system or are intended to form part of a filing system. (Article 2)
The GDPR applies to all businesses, organisations, authorities, clubs and individuals that are processing personal data (out of the private or domestic sphere). These businesses, organisations etc. are called data controllers.
The GDPR applies to data controllers in the EU and for all personal data that is being processed – this also includes persons that live outside of the EU.
The GDPR only applies to data controllers outside of the EU if these are offering goods or services to data subjects inside of the EU whether the data subjects have to make a payment, or they are observing the behaviour of data subjects so far as this behaviour happens inside of the EU.
Goods or services are being offered to persons inside of the EU if it is recognisable that persons inside of the EU ought to be reached. That can be done by prices in EUR, a website in a language especially spoken in the EU (like German or Czech) or by items which refer to an EU country.
An example: An US organisation that is selling online classes with no visible relation to the EU, is not subject to the GDPR – even if the online classes can be bought from inside the EU. If the organisation prices the classes also in EUR, then it is also subject to the GDPR.