Please read the API documentation. The developers resources page (http://www.clarizen.com/project-software-resources/for-developers.html) has some useful links to get you started. The documentation also contains basic samples.
Also check this forum for more samples (like https://success.clarizen.com/hc/communities/public/questions/203993638-Query-on-project-type-field-in-c-).
If you have specific issues we'll be happy to assist.
Hope this helps,