question about Twitter app or Twitterrific app.

Hi to all on the forum
I have a question about how to use the originalTwitter app
or
Twitterrific
I don't know those apps allot just to basic use but couple days ago I talked to some one on my list of following
and this contact want to follow or subscribe to some list who I am subscribed and to be honest I don't know how to add to this list,
some one else added to me at this list dot's y I don't know how to do it.
could some one help me on this way.
I use twitter app, Twitterrific, Chicken nugget or just the twitter clients .