Hi Adhvi,
Here is my understanding.
Catalog: It displays all runtime objects such as tables, SQL views, procedures, sequences which are grouped by different schema.
Content: It focuses more on modeling and design-time objects like XS stuff which are stored in the repository of SAP HANA. When you activate some XS stuff, e.g., .hdbdd and .hdbsequence, they will appear in catalog, since they are activated to runtime objects now.
Schema: As you said, it is like a folder which holds runtime objects like tables, views, procedures, sequences. Usually each user will have its own schema. If you want to have a look at the stuff in other's schema, you need corresponding privileges/roles.
Package: Like runtime objects can be stored in different schema, desing-time objects can also be placed in different packages/subpackages.
So in SAP HANA Studio, when you open Catalog, you will first see Schema; when you open Content, you will first see packages.
Best regards,
Wenjun