You can omit the low or high bound:
arr := [5]int{1, 2, 3, 4, 5}
slice1 := arr[:3] // [1, 2, 3]
slice2 := arr[2:] // [3, 4, 5]
slice3 := arr[:] // [1, 2, 3, 4, 5]
Omitting low defaults to . Omitting high defaults to length. Omitting both gives the whole array.