Welcome to DTS! I'll provide some basic initial answers, but please feel free to follow-up with any additional questions.
1. Yes, you can create your own namespaces. The basic process is:
A. Use the Namespace Editor (either standalone - Tools menu - or in the Details Panel) to create a new Namespace. You will likely want to create a Thesaurus Namespace.
B. Use the Attributes Type Editor (from the Tools menu) to create your Namespace's attributes types: properties like Code in Source, associations, etc. This is essentially the "schema" for your namespace.
C. Populate the namespace via the Editor, a custom API program or the Import Wizard plug-in (see below).
Once you have the namespace populated, you can create ValueSets (we call them Subsets) using the Subset Editor.
2. The Import Wizard plug-in (available from the Module Manager panel in the Option menu) can be used to import namespace data from text, Excel, or XML files. The XML file format is specific to Apelon (an xsd is provided) but import from text or Excel is quite easy. You would first use the Import Wizard to define a "specification" file, basically a map from Excel columns to DTS Attribute Types, then run the Wizard to automatically load all the data. A complete User Guide for the Wizard is available and will be loaded into your DTSinstall\docs folder once the plug-in has been installed.
Finally, for adhoc queries to your namespaces, we would recommend installing the Terminology Query Language (TQL) plug-in. TQL provides complementary export (and edit) capabilities to the Import Wizard's import functions. Specifically, TQL can create XML exports of your namespaces and subsets for exchange and backup.
Good luck! Please do get back to use with any additional questions.