This week's story happens nearly ten years after last week. Abram and Sarai still have no children and God's promise seems more and more unlikely to be fulfilled. They are too old and it's just impossible for Sarai to have a baby. Sarai tells Abram that clearly there's no way God can do what He promised and so they need to take matters into their own hands.
In their culture, it is acceptable to take more than one wife, and so Sarai tells Abram to marry their servant girl, Hagar, and have a son with her. That way, that son will be the heir that God promised. So Abram married Hagar and she became pregnant, much to Sarai's irritation.
God never wants us to try and help Him. When He promises to do something, He and He alone will fulfill it. He wants us to trust Him and let Him take care of it. When we try to help God out, we aren't trusting Him and we are doing things in our own strength, which is sin. And any time we try to help God out, we make a big mess. We'll see in the coming weeks just how much of a mess this makes.