The verb to make has various meanings in English, but the sentences that you are asking about all (roughly) refer to the same grammar rule, that is of causing, provoking a certain effect.
Generally, you use the construct to make someone do something to indicate that you oblige or force someone to do as you wish, or else that you cause something to happen; see for example
My father made me stay at home on Friday night.
That film always makes me laugh my head off.
If the object of the verb is a reflexive pronoun, then instead of an infinitive form we use a past participle, because the meaning is passive; with this construct you are saying that you allow, or make it possible for you to be understood/seen/heard by others. Hence your first sentence, which is very frequent.
In your third sentence you are using an adjective instead of a verb, which results in a perfectly grammatical sentence with the similar meaning to the first, i.e. that others can understand you, although it seems to imply some kind of effort, and it is not so frequently used.
Finally, the second sentence has a completely different meaning, because here it is you who manage to understand something, through clear effort on your part. To try and clarify, consider the following example :
I made myself understand her reasons for deserting me.