There are certain places within prayer, where we mention this interesting prayer. Just wanted to know why do we say Ana B'koach in those certain places?
This 42 letter arrangement, also called the 42 letter name of G-d, is actually related to the mystical intention aspect of prayers and is something that we are to meditate on at different points.
It is associated with the process of converting things from one state to another, in Hebrew called it’hapcha.
This type of activity is associated with the feminine which is also why the small sum gematria of the names of the 4 Matriarchs is also 42. (שרה, רבקה, לאה, רחל)
One example in prayer of when we are to meditate on this 42 letter name is while reciting the 2nd section of the Shema (the paragraph which begins v’ahavta), which contains 42 words. While pronouncing each word, one intends the corresponding letter from the 42 letter name.