In your command line, navigate to the directory that has your .jar file and run the following command...

java -Xmx3000M -Xms3000M -jar server.jar nogui

3000 is the amount of ram that we are dedicating to our server and is measured in Megabytes. You can also remove nogui if you want to use the GUI interface.

You may get a warning that says you didn't accept EULA. To fix this issue open the eula.txt file and set the eula variable to true