I can help.Well the verb to swim is "nadar" but "nada" means swims. "nada" also means nothing, so you can't really tell the difference between them. You can only really understand the two apart when the word in a sentence. For example if i would say "Mi madre nada más que mi padre"and you thought it was my mom/mother has nothing more then my dad/father it would make sense, but "Mi madre nada más que mi padre"makes more sense.Hope this helps.
Than is always used to compare two things and is preceded by an adjective:
She is prettier than her. He is smarter than his brother.
Then is always a consequences of a situation. If (this) happens, then (that) will happen as a result.
If I am late, then I will fail.
You don't have vanilla? Then I will have chocolate.