SSIS consists of several components that are designed to interact with each other and designed as independent blocks of functionality.
Pic 1: SSIS Architecture Diagram
First component we want to look at is called SSIS Designer. SSIS Designer is a graphical User Interface that sole purpose is to support SSIS packages. It is part of BIDS and it is available from SSIS Project
Second component we are looking at is Data Flow Task component that is designed to provide buffer that are utilized for moving data from data source to destination. The Data Flow Tasks is also designed to handle majority of ETL related activities.
Third component we want to examine helps with monitoring health of SSIS. It is called Integration Services Service. It is designed to work with SQL Server Management Studio. Finally, Object Model is an important part of SSIS. It includes API that allows creation of custom application to run and execute SSIS packages.
There are other SSIS components as identified on Pic 1. They are all integral part of any SSIS implementation and you need to know them as well.