From is a preposition, a small word placed before a noun to show where something starts or comes from. She flew from Rome to Oslo.
From marks the starting point of a movement or stretch of time, and it always sits before a noun or pronoun to do that job. In She flew from Rome to Oslo, the word from points to the place where the journey began. It works the same way with time: the trip starts from Monday. In every case, from answers the same quiet question: where, or when, did it start?
In sentences about places, from points to the starting point. Picture a train pulling out of a station: The train to Leeds comes from Manchester. Manchester is where the journey begins.
In sentences about time, from marks the moment something starts. A shop sign might read: We are open from 9 a.m. to 6 p.m. Nine in the morning is when the opening hours begin.
From as the usual choice for a stretch with an end. When the period of time has both a start and a finish, from is the natural word. It marks the opening edge of that stretch, as in We are open from 9 a.m. to 6 p.m., where from 9 a.m. names the start and to 6 p.m. closes it off. A related word, since, behaves differently: it fits only a single point in time attached to a situation that keeps going, such as I've lived here since 2019. So if the situation is ongoing, since is the fit; if the stretch has an end, from is the usual choice.