You should be navigated to the Install Required Plugin page, which shows reqquired plugins list, all you need is clicking on the checkbox beside "Plugin" label to select G5 Core, G5 Service in the list, then choose "Install" from the drop-down list at the top and then click "Apply".
You can do the same as installing, After you install successfully,you select that two plugins to active .
After you install & active G5 Service plugin, G5 Core plugin successfully, the Service settings start to display
The Service items are included Service post type, Service settings, Overwrite Theme options for Service
1- Service post type are options register a custom post type for Service items. It also registers separate Service taxonomies for tags and categories
2- Service settings are settings for layouts, gallery etc in Archive Listing and Single Service
3- Overwrite Theme options for Service are settings for layout, page title, header, footer, color and typography in Archive Listing and Single Service. This settings overwrite the same setting in Theme option