Where does it say that the Hebrews/Jewish people should celebrate Chag Ha-Matzot, also known now as Passover or Pesach ?
In the Hebrew Bible, Chag Ha-Matzot (now known as Passover or Pesach) is either mentioned or commanded by G-d to be celebrated by the Hebrews in: Shemot or Exodus 12:17; Shemot or Exodus 23:15; Shemot or Exodus 34:18; Vayikra or Leviticus 23:6; Bamidbar or Deuteronomy 16:16; 2 Chronicles 8:13; 2 Chronicles 30:13; 2 Chronicles 30:21; 2 Chronicles 35:17; and Ezra 6:22 .
The name Chag Ha-Matzot symbolizes the belief of the Hebrews in the One, True G-d, since during the Exodus from Egypt, the bread baked by the Hebrews to take for their journey out of Egypt did not leaven - and so it was unleavened bread, known in Hebrew as matzo - just before G-d appeared before the Hebrews and redeemed them from Egypt. Therefore, the symbolism and significance of matzo - and, by extension, Chag Ha-Matzot - is that matzo is associated with the historical point in time during the Exodus from Egypt whereupon the Hebrews saw that the One, True G-d would indeed rescue them from slavery in Egypt, and so their belief in the One, True G-d was consolidated.
In addition to Chag Ha-Matzot, there is another festival name that is mentioned in the Torah (Shemot 34:25 or Exodus 34:25), and this festival is connected to and associated with Chag Ha-Matzot. This festival's name is Chag Ha-Pesach ["The Festival of the Lamb" in Hebrew, with "lamb" in this context referring to the special lamb set aside to be sacrificed specifically for this festival]. Chag Ha-Pesach is connected to and associated with Chag Ha-Matzot because it occurs on the 14th day of the first Hebrew month of Nissan or Nisan, which is the day before the first day of Chag Ha-Matzot, which begins in the evening on the 15th day of Nissan or Nisan. Chag Ha-Pesach symbolizes the exalted status of the Hebrews/Jewish people in relation to G-d, and this was demonstrated during the series of ten plagues that culminated in the Exodus of the Hebrews from Egypt. As each plague occurred, G-d continuously smote the Egyptians while continuously sparing the Hebrews, and this difference of status between the Hebrews and Egyptians in relation to the One, True G-d reached its peak during the 10th and final plague, when G-d destroyed each first-born in every Egyptian household, but chose to "skip over", "jump over" or "pass over" the households of the Hebrews after seeing the blood of the sacrificial lamb on the two doorposts and lintel (the beam above the door) of each Hebrew household, as the act of spreading the sacrificial lamb's blood on the two doorposts and lintel was commanded by G-d via Moses to the Hebrews, and it was a prerequisite to G-d skipping, jumping, or passing over the households of the Hebrews. In fact, the Hebrew word Pesach refers to the skipping, jumping, or passing over of the Hebrew households by G-d, and so this particular action done by G-d - this Pesach - demonstrated the exalted status of the Hebrews in relation to G-d, resulting in Chag Ha-Pesach being associated with and symbolizing the Hebrews/Jewish people's special status with the One, True G-d.