Hey,
See the below example,
> superstore$Order.Date[1]
[1] "2014-11-11"
> seq(superstore$Order.Date[1],length.out = 5,by = "day")
[1] "2014-11-11" "2014-11-12" "2014-11-13" "2014-11-14" "2014-11-15"
length.out is the increment, by is increment based on what part of the date.