Hi Pawan,
As mentioned by swarna, the objects in the content folder are design time objects (created in "project explorer")and these design time objects are later activated to create run time artifacts, you can see these run time artifacts in the "Catalog".
Design time artifacts can be seen as a defination for run time artifacts.
Creating design time objects helps in maintaining the source code, transportation of source code between different systems(in the form of delivery units) like from Dev to testing and from testing to production.
Examples of design time artifacts are files ending with .hdbprocedure, .attributeview, .xsodata or .hdbdd files, you usually create these files in project explorer and on committ these files are copied to repository i.e., under "content" folder. These files are later activated to create run time artifacts.
Examples for runtime artifacts would be the tables, procedures in the catalog.
Regards,
Vijay.