Step 1: Changing dates to years
First you can change your column of dates (Order_Date) to simply years by using this formula:
> salesdata$Order_Date = format(salesdata$Order_Date, "%Y")
This will give your Order Dates just the year the sales was done in.
Step 2: Summarizing your sales data
After this you can create a vector with the summarizations of your sales data per year. This can be done using tapply:
> tapply(salesdata$Sales, salesdata$Order_Date, FUN=sum)
This will give you an overview of the total sales per year.
Step 3: Plotting your graph
You can use barplot() to plot your bar chart using the values you got in your tapply function.
The function as a oneliner:
> barplot(tapply(salesdata$Sales, format(salesdata$Order_Date, "%Y"), FUN=sum))
Of course you can edit your graph to your liking.