In the Tools menu, go to Message Rules and select Mail...

Looking at the top box 1. Select the Conditions for your rule, you will see you have many choices in the scroll box. Scroll down and select one which you would like to use by clicking in the small square box to the left of the condition. For example, if you choose Where the from line contains people, then any message which is from a certain user (which you can specify next) will be tested.

In box 2. Select the Actions for your rule, you again have several choices in the box. Scroll down and choose one in which you want the program to do when it encounters email that fits rule #1 above. For example, if you clicked on the square box next to Move it to the specified folder, any email that contains a certain email address or sender will be automatically moved to a folder which you will choose below.

Now we specify the details of the rules we created above. Click on the blue link in box 3. Rule Description which says contains people. A Select people box will pop up. Type in the email address or name that you wish to filter out. Click on the Add button and it will be added to the People: box below it. When done adding addresses, click the OK button. You will see the address added to box #3.

Click on the blue link in box 3. Rule Description which says specified folder. A Move box will pop up. You can use the New Folder button to add a Junk Mail folder to your in box. Then click on the Junk Mail folder and click the OK button. You will see the Junk Mail folder added to box #3.

Finally give your filter a name and click the OK button. Your filter is now ready to use. Anytime you get email from the address you typed in, it will automatically be sent to the Junk Mail folder you set up.