Does someone know if the series “Agents of Schield” play in the MCU?

Yes buddy, Agents of Shield is a part of MCU

I think most of the Marvel series’ are part of MCU

It is set in the MCU and recognises the continuity of the franchise’s films and other television series.

Yes it is the part of MCU. As for hint agent Coulson is in both series and movies.so they both are connected.

Yes it is oldest series of MCU