The Present Progressive Tense

Uses:
1. Actions happening ate the moment of speaking;
The students are listening to the teacher now.

2. Futurity;
I am flying to Paris tomorrow.
He is going home next week.

3. Temporary habit;
He is dieting this summer.

4. With 'always' for a frequently repeated action;
Tom is always going away for weekends.

5. Common adverbs used with this tense:
- now
- at present
- at this moment
- still

Special Notes
The are a number of common verbs wich do not often use in the Progressive Tense when we are describing an action at the moment of speaking. These verbs are generally used in the Present Simple Tense because they describe which cannot be stopped or started at will.
These are the principal verbs of this type:
- Verbs of the sense: see, hear, smell, notice, recognize, feel, taste
- Verbs of emotion: want, desire, refuse, forgive, wish, need, hate, love, like
- Verbs of mental processes: think (opinion), believe, understand, know, mean, suppose, remember, mind
- Verbs of possession: own, owe, belong
- Seem, appear (=seem), contain, consist

I believe he is telling the truth
I understand what you are saying