Indicative talks about facts while subjunctive talks about wants, beliefs, needs, feelings, emotions, etc.. The sentences below will illustrate this difference.

Indicative
Yo tengo que estudiar las palabras.
I have to study the words.
Subjunctive
El profesor quiere que yo estudie las palabras.
The teacher wants me to study the words.
Indicative
Tú tienes que estudiar las palabras.
You have to study the words.
Subjunctive
El profesor quiere que tú estudies las palabras.
The teacher wants you to study the words.
Indicative
María tiene que estudiar las palabras.
Mary has to study the words.
Subjunctive
El profesor quiere que María estudie las palabras.
The teacher wants Mary to study the words.
Indicative
Nosotros tenemos que estudiar las palabras.
We have to study the words.
Subjunctive
El profesor quiere que nosotros estudiemos las palabras.
The teacher wants us to study the words.