Hi Adarsha,
When we attach the workflow to a library or list, all documents in that library can be assigned to that workflow. Please refer to the following steps to create the workflow.
1. Open the SharePoint site from 32-bit IE browser.
2. Click Site Actions> Click Edit in SharePoint Designer
3. After opening the SharePoint Designer, click List Workflow.
4. Select a Library or List, and then enter the workflow name.
5. Input the rules you would like to.
6. Click workflow settings, select the start options.
7. Click Publish.
For more information about how to create workflow in SharePoint Designer, please see: http://office.microsoft.com/en-us/sharepoint-designer-help/video-create-an-approval-workflow-in-sharepoint-designer-2010-VA101897477.aspx
Thanks,
Keats Ge