Nahash, the Ammonite king, besieges Jabesh-gilead. When the people of Jabesh-gilead attempt to make a treaty with Nahash, he has a condition for the treaty. He must be able to gouge out everyone's right eye. Yes, because that makes sense (1-3).
When Saul hears this news, he's so outraged he slices up his oxen and sends pieces to every tribe in Israel. The message: come fight with me or all your oxen will be cut up, too. Point to Saul (4-7).
Saul, unsurprisingly, assembles a huge army. After some when and where dealings, the Israelites swiftly defeat the Ammorites in battle. Saul has now proven himself in battle, something the tribes of Israel needed to see from their new king (8-15).