You need a checkbox group and then use the Validation to set the appropriate requirements. First take a checkbox field and add it to the document, then click that new field and you should see a "+" appear under the first checkbox, select the "+" to add another checkbox to that checkbox group, continue until you have all the checkboxes you need. Place them then select any checkbox and go to the right panel under Validation. Here you can select the minimum or maximum such as Select at Least "1", which requires one but also allows for more than 1 or all to be selected. Save or Send depending on whether this is an envelope or Template.