how to understand db in audacity?

how to change my voice file into 28db in audacity?

There’s different methods of measuring your voice, so we need to know what the job is, which microphone you’re using and any other details about your system. Audio Interface or USB microphone?

For example, Audiobook reading needs to measures the RMS, or overall energy of your voice, but Effect > Amplify and Effect > Normalize work on second by second loudness events or peaks. They’re different enough that you can’t cross the tools, so knowing the job is important.