Different versions of Excel create charts differently, but I can give you a general idea of how to do it.
1) Build a table. If you want to graph something by days and hours, then your table should be rows of days and columns of hours. Insert your data points in the table accordingly.
2) In the toolbar, select “Insert -> Chart”. If you are in 2007 or 2010 there are menu buttons for different types of charts in the toolbar. Either way, this will bring you to a wizard. For data source, select the entire table you created in step 1. This will create the graph/chart
3) Select an empty point inside the graph and right-click. This will bring up an editing menu for the graph, where you can set things such as axis labels, increments, titles, etc.
Click around a bit until you find exactly what you need or use Excel help (F1). If you ask for help here you need to get much more specific.