I'll explain how dates in Excel work and then point you to many useful tutorials on how to use dates and also times in Excel.
Dates in Excel are actually just numbers that are formatted as dates.
If you take a date and select the cell and then set that cell's formatting to "General" it will look like this:
Cell A1 has the "date" and cell A2 has that same date formatted as "General."
As you can see, Excel stores dates in this weird format, but, it's actually not that weird and makes handling dates a lot easier. Excel stores dates as numbers.
The dates actually start at January 1, 1900, which is represented with a 1, and add one for each day since then. So Feb 10, 2016 is 42,409 days since January 1, 1900.
Look at what happens when you format 1 as a date (it appears as the date 1/1/1900):
The point to learning that dates are just numbers in Excel is because, then, you can more easily remember how to manage them.
Add a day to a date by adding 1. Add a week by adding 7.
Cells A4 and A5 show the formulas entered in cells B4 and B5.
As you can see, storing dates as numbers makes dates easier to work with because we can use simple math to adjust them.
This is just an intro to help you wrap your head around the concept of dates in Excel. There are many more complex things that you can do with dates and also with times in Excel.
Here is a link to all of our date and time tutorials: Date and Time Tutorials for Excel
There is a lot to learn about dates; make sure to check out the link above to see all of our tutorials on that subject.
Download the accompanying spreadsheet so you can see the examples from this tutorial in Excel.