What is the explanation of the uvdin dechol in shabat, how can i know what things that doesn’t have a melacha are uvdin dechol and what things aren’t uvdin dechol.
The matter of uvdin de-chol is a complex issue, as we find from the varied rulings given by poskim for many related questions.
The based principle is that matters that are related to a melacha, or matters that involve some denigration of the holiness or spirit of the day, are included in the category. Thus, it is forbidden to engage in commerce and to weigh foods, to carry jugs of wine from place to place (in the regular manner), to grind spices with a grinder, and to gather scattered fruit into a bag.
The definition is somewhat vague, leading to some lack of clarity in this subject. For instance, the Shulchan Aruch Ha-Rav (328:47) writes that vigorous massage is forbidden on Shabbos because this is considered uvdin de-chol (the ruling is based on the ruling of the Shulchan Aruch in siman 327 (2); see a separate post on this subject).
When a question comes up on this subject, it is best to consult with a knowledgable authority.