Hi Sarviin,
happy to help you here: In general a Executive sponsor is a person in senior management or even the board that initiated (sponsored) the project, e.g. because the project is one of his priorities, he freed up some budget for the consulting projects, etc.
The Steering committee typically consists of several key experts / managers at your client and is used to report on your project and take relevant decisions (it´s typically a 0.5-2 h meeting ever few weeks), e.g. to ensure the right scope towards other projects in the organization and agree on next steps.
Hope that helps,
Simon