As we have already downloaded and installed the Appium Version 1.8.1. Once You open it, it will gonna looks like as in below screenshot. Now, You have to start Appium server by clicking on Start Server button.
Once you click on Start Server button, it will start Appium Server at default IP address and port number(0.0.0.0:4723). You can change the IP address and port number, if required. Just have a look at below screen shot.
After starting the Appium Server, next step is to create Appium script. Kindly refer next post to get to know about creating first Appium script. CLICK HERE
NOTE : In this post, we have started the Appium Server using the Appium UI, However, you can also use command line to start/stop the Appium Server. Kindly refer following link to get more information about it. Start Appium Server from command line