When writing code, most developers like to see problems and code smells directly in their code, without switching to an external window or panel.
How to enable the linter?
You can install these packages directly from atom as any other package.
Once enabled, Molecule will provide diagnostics to the linter plugin you installed.
Most plugins that interact with the code (static analysis, unit test, code linters) provide them and you'll be able to see their diagnostics directly into the code.
For more details about how the linter works, please refer to the documentation of your linter package.