Creating a new Minecraft server

In the sidebar to the left click on the Add More button then click on Minecraft Java

You will now be asked to name your instance, once you have entered a name click on Create

In the next screen you will be asked to select a version to install, On this screen you can search for the modpack you want to install and select the version of the modpack to install using the dropdown to the left of the install button. Once you have found the modpack to install and selected the version you want to install click the Install button.