Use of three verbs: Understand, Believe and Agree

1. Understand: I understand it (just after the explanations by the teacher, I say this). My question is: does it fall into a speech act I mean, is it used as a stative ( mental state) verb or performative (mental event) verb?

2. Believe: I believe what you are saying now (I use this verb at the moment speaking). the Same question as above?

3. Agree: I hesitate to apply for this post because of the risk involved. My friend says, "I agree." (My friend uses this verb during this conversation). the Same question as above?