1990 jeep wrangler when you try to start it it will make a clicking noise under the hood battery is fine what else could it be?

Could be several things but you need to check the terminals on the battery for good connection, the cables coming off your battery for signs of corrosion, and if all those check out and you know you are getting plenty of power to your starter solenoid then you have a bad starter solenoid. Basically inside your starter is a contact plate that tends to get corroded, if it gets to bad then it will not give your starter enough power to actually turn your engine over. However, it will give enough power to try and activate your starter hence the clicking sound. Sometimes you can hit your starter with a hammer to try and shake some of the rust or buildup inside your starter free and it might let you start your car.