Different types of objects could be inserted to MS Office documents including pictures, spreadsheets, sounds etc. There is two options: you can embed the object or link it. Embedded objects don't reflect changes of the sourse files while linked objects do.

Linking means your two documents are linked, as in connected to each other. You have your original file (source), and you have a second document (destination) where you linked the first file (source). You can maintain the connection between the two. When you update the original (source) document the second file (destination) is updated as well.

For example create graph in Excel. Copy the graph by using right click on the graph.

Go to PowerPoint and place in on a slide. Use the edit menu and select Paste Special.

Choose Paste Link and click OK.

Now you can update numbers in Excel. Both copies of the graph will be updated.