I saw a lot of bassist that using a kind of cloth. They are just packing it in the bass case and hold it sometime, but i didnt understand ehat are they doing with it. Do they take care of yhe bass sith that cloth?
Sith cannot be taken care of by a mere cloth. It requires jedi powers. Also stop typing with your feet.
Cloth in bass case. To clean the bass, front, stings and neck after an evening of sweating and handling. My Daddy always told me, "Clean your tools after you use them, then put them away" I use a gray terry cloth wash cloth.
Welcome to the forum. No, it's only kept for wiping down your instrument. Some people do it after playing, some during string change out, some don't. Up to you. You could find one cheap if you want one. guitar polish cloth - Google Search
Micro fiber cloths are good because they don't leave lint and threads don't get caught in the strings. They also dry quickly. They are special.
Welcome to TalkBass!!!!! Can you describe it? They may have a microfiber towel for wiping their basses off? I have a little tiny rag that comes in every Fastfret for wiping off strings. Some guys just wipe down their strings with a washcloth. Could be anything. But there is no one particular cloth that all of us keep around for a special reason.
A lot of bassists/guitarists use flannel cloths for polishing, like this: https://www.wwbw.com/Music-Nomad-Al...uH70798000000000&rNtt=Polishing cloth&index=6