To set a baseline for selected tasks and roll up all summary tasks, in the desired project, select the desired tasks and summary tasks (using the Shift or Ctrl keys), go to menu Project – Set Baseline – select the desired baseline from the Set Baseline field – check the Selected Tasks option. From the Roll up baselines section check the “From subtasks into selected summary task(s)” option and click OK. The baseline fields for the selected tasks will be updated with the baseline values and only the selected summary tasks will be updated.