I have Tasks list in my SharePoint website and each task is assigned to a person based on a workflow. I want the tasks to be visible to the users only if they have been added to the workflow.
Assuming the task list in displayed in a web part and you want to filter on assigned to:
Edit the page with the task list
Edit the web part and change the Selected View to My Tasks. This will filter the task list to only show tasks assigned to the current user.
If you need to filter on other columns you can create a custom view to display what you want. Then change the web part to use your view.