Click on the Activity Custom Fields tab from the menu on the left.
Click on Add to create the new field.An item called New Field will be added to the page. Click on the words New Field to edit the name. From the drop-down menu, select the type of field most appropriate for the data you wish to capture.If you choose one of the Selection fields, for example Selection (Multiple - Checkboxes), you will be able to add the options by clicking on the Add your options text. Click on Add Selection within the pop-up window.Enter the title of the option and click on Confirm.Repeat until you have finished adding all the options then click OK.