There are various commands you can use with Snyk on the command line and they all do different things. For information about all of the Snyk CLI commands use the command snyk help.
The snyk test command scans your project, tests dependencies for vulnerabilities, and reports how many vulnerabilities are found. The command returns a non-zero exit code which causes a build to fail when run inside of CI environments (depending on how the CI tool is configured).
The snyk protect command has been replaced by the @snyk/protect package. This package applies the patches specified in your .snyk file to the local file system to patch your vulnerable dependencies. This is useful after opening a fix pull request from the Snyk website (GitHub only). See the README for information on how to use the package and how to migrate from snyk protect.
You can use the snyk monitor command to create a project on the Snyk website to be continuously monitored for new vulnerabilities. After running this command you see the project by logging in to the website and viewing your projects.