Malo/a are adjectives for describing. Usually means "bad". And the differences between Malo and Mala is the gender. For a feminine form is Mala, for a masculine form is Malo and before a singular noun used Mal instead. Ejemplos:
"Mi celular está malO, no recibe llamadas" — My cellphone is broken (bad), it's not receiving calls.
"Esta comida está malA" —This food's bad.
"Tengo UN mal presentimiento" —I have a bad feeling.
"Tengo UNA mala noticia" — I got bad news. (One bad new)
"MalAS noticias: Trump quedó presidente" —Bad news: Trump got elected.
Mal is an Adverb. Means "Badly" "Wrong" "Not good" "Poorly". Used with verb Estar instead of ser. Ejemplos:
"Juan lee muy mal" —Juan reads badly.
"ESTÁ mal hacer eso" —It's wrong to do that.