What forms do I need to fill out to legalize a parent who entered the country legally? i.e. agricultural visa, but, the visa has expired?

In what country?. in the USA they are going to have to leave... apply for a new Visa.. and if they get another come back... you can't simply fill out forms for someone who is illegal and make them legal.

And they are illegal... as their VISA is expired... they had to either renew it BEFORE it expired... or leave before it expired.

Are you a U.S. citizen over 21? If so, your parent can adjust status here. You guys should file I-130, I-485, and I-765, all in the same package (you fill out the I-130, and the parent fills out the I-485 and I-765). If the parent has overstayed for a long time, the parent should not leave the country until they get the green card.