Jeff, the son of a farmer, wants to marry Millie and tend his late father's farm. He likes the idea of working the land and being part of the land. It makes him feel like he's part of something bigger.
But mom, Carrie, has other ideas. She is panicked at the idea of her son living the same kind of life that she did. Apparently she feels like her entire adult life was wasted. That her husband let her down and that life was drudgery. She always wanted to go to the big city and see "the far places" and she is determined Jeff will do just that. But he doesn't want to do just that.
What a go mom. Tell the lad his father was a failure and that raising the lad himself was an entirely inadequate consolation prize versus the rewards of regularly going to whatever passed for Happy Hour in Chicago in 1875,
Not content to stop at withering criticism of her son's life plans, she decides to put an obstacle in his way. She will sell the farm out from underneath him. Jeff's dad's will gave Carrie ownership of the farm until her death, and then it reverted to Jeff. Since Carrie currently is the legal owner she intends to sell it. When that doesn't work out, she has one more plan to stop Jeff that involves Jeff's girlfriend/fiance. If you want to know what this plan is, watch and find out.
The actress playing Carrie seemed unjustifiably overwrought while the actor playing her son seemed understated for the most part. Sometimes you just need to let the young people make their own plans and their own mistakes after you've given them the best advice that you can.
I will say that mom had a perhaps correct but uninformed opinion when it came to Jeff's fiancee. She seemed hungry for a constant parade of new experiences. If she married Jeff and was plunged into the ennui of daily life as a farmer's wife, I can see her becoming as bored and eventually angry as Jeff's mother, Carrie, was.