When the sun moon and earth are aligned, ocean tides are larger-high tide is higher, low tide is lower-than when they are not aligned. How might this relate to gravity?

When the sun and the moon are aligned, or nearly aligned, their gravitational gradient fields add together constructively, leading to extra strong tides (high tide is extra high and low tide is extra low). This alignment happens when the moon is a new moon or a full moon, which occurs about every two weeks.