You can go to new compound creator study, then create your own database using the Create New option. A new xml file will be created. After than you can create the new compound by entering the required properties. Then click on the option Save compound to the database and then save the simulation. Now go to settings-->general settings-->Datasets and click on Add User database. Search the xml file for the new database you have created and add it. The next time you start DWSIM you will find the compound. Alternately you can add the compound to an existing database like Chemsep or DWSIM. The procedure is same except that in the new compound creator study instead of creating a new database click on Search and select the xml file for the database (chemsep.xml or DWSIM.xml) which will be there in DWSIM's installed folder.