Hi @Chamepp,
Specifically if you want to participate in GSoC for 2025, you need to submit a project proposal before April 8 at 18:00 UTC (next week).
If you're interested in improving command line tool documentation and are already familiar with the code base I would suggest writing up a description of the improvements you want to work on and a breakdown of that work. The Google Summer of Code Guide contains general, good advice about writing a project proposal.
You might also find some relevant information in this other thread and possibly in this message.