Hi William,
The basic idea is that SonarCloud does not perform coverage analysis itself. It relies on you setting up a coverage tool (like Jacoco, for Java), having that tool run on each build, before the SC analysis is performed.
SC is then configured to pick up that coverage report on each analysis, process it and display the data as partof its results.
Have a look here for some guidance: [Coverage & Test Data] Importing JaCoCo coverage report in XML format