Steps to follow in order to simulate a VHDL model with ModelSim PE Student Edition:

1. Start ModelSim
2. From menu File select Change Directory (we will denote this sequence of operations as "File -> Change Directory") and select the directory, for example C:\Student
3. File -> New -> Library
   
   A new window, called Create a New Library, pops up. If the working directory does not contain a previous library, then in the Create New Library window, you will see:
   
   Library name Work and Library Physical Name Work. Do not change these names, just click Ok. If a library Work already exists, then you may use it, and don't need to create a new library. Otherwise, you will see in the Library window a the library work (empty).
4. File -> New -> Source -> VHDL and a new window will appear, offering you the possibility to edit a VHDL program.
5. Edit the VHDL program
6. Save the file with a name and with the extension .vhd or .vhdl (e.g., cad1.vhdl )
7. The vhd file(s) must be in the same directory with the library WORK
8. DO NOT save the vhd file(s) in the directory WORK !!
9. Go to menu Compile -> Compile. Normally you should see the .vhd and/or .vhdl files from the working directory (i.e. C:\Stuent )
10. Select your file and compile it.
11. If you have errors, try to remove the errors, save the file again and reocmpile the file. Do this until you remove all errors.
12. After you compile all your source files, in the library window you should see, to the left of the library work, a small rectangle with a "+" inside it. Click on the + and you will see the entities that you compiled.
13. In order to start the simulation, you can select the Simulate menu, or you can double click on the top-most entity of your design (from the library window). Normally this is the entity that "links" all your entities and it should not have inputs. It is recommended to be a test bench.
14. If your simulation model is correct, then new windos will appear. If the ModelSim licence has expired, the message will be "error loading design", but this error message can have other causes (e.g., errors in the model).
15. In the window named sim, select the top-most entity (e.g. test_bench) and right click from the mouse. From the menu that appears, select Add Wave.
16. A new window, named Wave - Default appears. You will see the signals from the top-level entity.
17. In the main window, change the Run length value from 100 ns to a value that suits you (e.g. 2000 ns). You may also leave this value unchanged and increase the simulation length in 100 ns increments (see next step).
18. In the main window, select the Run icon (situated to the right of the Run length). When you click on the Run, you will see that the selected signals have been simulated and displayed for the selected run length. If you repeat the operation, the simulation model will be simulated for another selected length (e.g., for another 2000 ns in our case).
19. Click with the mouse inside the Wave window and then select the zoom that suits you (from the main window). You can see eithter the entire simulation period, or only parte of it.
20. Try to understand the evolution in time of the simulated signals and see if your simulation model was correct.