You can combine your bardic performance and your spellcasting in two ways. First, you can conceal the activity of casting a bard spell by masking it in a performance. As a swift action, you may combine your casting time of a spell with a Perform check. Observers must make a Perception or Sense Motive check opposed by your Perform check to realize you are also casting a spell. This uses 1 round of your bardic performance ability, regardless of the spell's casting time.
Every bard spell has a verbal component (singing, reciting, or music).
A verbal component is a spoken incantation. To provide a verbal component, you must be able to speak in a strong voice
A somatic component is a measured and precise movement of the hand. You must have at least one hand free to provide a somatic component.
Just how does dancing (or miming, which is a possible use for act going by The House of the Imaginary Walls, for that matter?) mask verbal components? Same with singing for somatic stuff.