The European XFEL (XFEL.EU) is a research facility open to scientists worldwide. Beamtime is free of charge, but experiment proposals must go through a review process. Proposal submission must be done through the User Portal to the European XFEL (UPEX). As an important condition for access, after the experiments, the authors must strive to publish the results in peer-reviewed journals. This guide describes how scientists can register in UPEX and submit proposals for beamtime. This guide describes how scientists can register in UPEX, submit proposals for beamtime, register for an experiment, and confirm the samples and substances used in the experiment via the UPEX Arrival Form (A-form).