Behold is a verb that means to look at something, to observe or see it. The past tense is beheld. Someone can be a beholder. It is often used in command form, telling someone else to Behold!
Beholden is an adjective that means to owe someone something, to be obligated or in debt.
There is no clear evidence as to why beholden has such a different definition than the word from which it originated. Only that beholden did in fact come from the past participle of behold.
Another idiom attached to this word lo and behold, which originated as an interjection of awe or surprise. Now it is most often used in jest in describing something that shouldn’t be surprising at all.