“Amidah” means “standing.” When reciting the Amidah, the centerpiece of every service, we stand with our feet together in order to be more angelic (as the prophet Ezekiel described the angels, having fused legs). The Amidah consists of a series of berakhot, poorly translated as “blessings,” to each of which, when said aloud, we say “amen,” meaning “so be it.”
When we begin the very first blessing, we bend our knees and then bow from the hip during the words “Barukh Attah,” “Praised are You.” We do the same at the next “Barukh Attah,” which concludes the first section and signifies our respect for our ancestors’ relationship with God.
When we reach the blessing “Modim anahnu Lakh,” “We are grateful to You,” we bow from the hip, thanking God.
And when we end that blessing with “Barukh Attah,” usually just before the Priestly Blessing, we once again bend our knees and bow from the hip.
Our prayer book Siddur Lev Shalem has red markings indicating when to bow, a total of four times.