Fieldsets are cool. They group a bunch of fields together. You can control a whole block at once too!

Go to Marketing Activities.
Select your form and click Edit Form. 
Click the + sign and select Fieldset. 
 
Select the fieldset and enter a Label.
Drag the fields you want into the fieldset. 
Here's what it should look like when done. 

There you have it!

You can dynamically hide/show the entire fieldset depending on another field. Learn about visibility rules.