The MakeHuman mesh comes into Blender completely naked. There are plans to make clothes within MakeHuman in the future, but for the time being you must dress him yourself. It is a good idea to do so e.g. if you plan to show your work on Youtube, which has problems with nudity.

There are several ways to dress the character:
1. Paint clothes on the texture (the file "texture.tif") in a program like Photoshop or Gimp, or using Blender texture paint tools.
2. Model clothes in Blender and parent them to the armature.

This is not meant to be a tutorial on how to model clothes in Blender; many excellent tutorials are available on the internet. Once you have modelled the clothes, you want them to move with the rig. How this should be done

To attach a rigid object like a hat to the character:

Parent the hat to the head bone: select hat, also select head bone, Ctrl-P, choose "Make parent to bone" from the popup menu.

To attach a deforming object like a suit:

Parent the suit to the armature: select suit, also select the armature HumanRig, Ctrl-P, choose "Make parent to armature" from the popup menu.
There are several ways to weight the suit.

1. Use automatic weights from bone heat. Choose "Create from bone heat" in the popup menu.
2. Project the body weight with the Bone Weight Copy script. This can be found under the menu Help > Scripts Help Browser, and then Object > Bone Weight. Copy. Choose "Don't create vertex groups" in the popup menu when parenting, since the vertex groups have already been created.
3. Paint weights using Blender's vertex paint mode.
4. Create vertex weights manually in edit mode.

It may be a good idea to delete parts of the body that are covered by the suit, both to boost performance and to avoid that the body peeks through the suit.