To create a BAK backup, do the following steps:

1.  Shrink the Database (Optional)

1. Open Management Studio and connect to the database server.
2. Change the Recovery Model to Simple
   1. Right click on the database you wish to backup and select Properties.
      
   2. Click on Options.  Write down the Recovery Model of the database, then change it to Simple and click OK:
      
3. Shrink the Database
   1. Right-Click on the database, then select Tasks > Shrink > Database.
      
   2. Check "Reorganize files..." then click OK.
      
4. Restore the Recovery Model
   1. Follow the steps above to restore the recovery model back to its original value.

2.  Enable Backup Compression (Optional)

1. Right-Click on the Database Server and select Properties.
   
2. Click on Database Settings, Check "Compress Backups", then click OK
   

3.  Take the Actual Backup

1. Open Management Studio and connect to the database server.
2. Right click on the database you wish to backup and select Tasks > Back up...
   
   
   
3. In the dialog that appears confirm:
   1. Database you have selected to backup
   2. Backup type: Full
   3. Backup Component: Database
   4. Back up to: Disk
   5. Click "Add..." to select your backup destination
      
      
      
      
4. In the dialog that appears click the ellipse "..." button
   
   
5. Select your BAK backup destination and file name. Click OK:
   
6. Click OK on the "Select Backup Destination" dialog:
   
7. Confirm your backup destination and click OK:
   
8. Your BAK backup is complete!