1. Go to CRM Settings option.
2. Under 'Automation' click on Workflows.
3. Click On Add a workflow option.
4. Add a suitable name so that you can refer to in future for which purpose the workflow is created.
5. Select the 'Lead' as an entity amongst the given entities.
6. Select action and trigger preferences as given in below image.
7. Select 'All leads' in condition and choose 'Create Task' as an option in set actions to be performed.
8. Add the details which are required in Create Task option and then 'Save & Activate' the workflow.

Once this workflow is created then we need to create another workflow in which we will associate this particular workflow to trigger as expected in condition.
9. Click on 'Add a workflow' & Select the 'Call Log' as an entity amongst the given entities.