When you mark a job as In progress in your list of jobs, you see that a grey circle appears next to the status of the job.
You can click on this circle to indicate your progress in the job (e.g. if you already translated 20% of the job, or 50 or 75%, etc.)
The circle will be filled in with green depending on the progress you defined. The circle will be half full if you typed '50%', for example.
You can also change your progress in the job itself, by clicking on the circle in the Overview panel of the job.
If you're using LSP.expert V1
When you mark a job as In progress, you'll see a green dot below this job in the list of jobs.
You can click on this dot to indicate your progress.
A green line will then appear under the job, indicating your progress, so you always know where you are in this job. The line will be half full if you type '50%', for example.
You can also change your progress in the job itself (there is a Progress field).