Create and Configure the Search Service Application in SharePoint

You can create and configure the Search Service Application either manually or through Powershell Automation

Go to CA -> Manage Service Application -> Click New Search Service Application

Enter proper name for Search Service App

Create a Service Account in AD. Enter a new App Pool and select service account. Click on OK button. Now Search Service Application will be created.

When search service app is created, following 3 databases will be created in the database server

Administration Database 
Crawl database 
Property Database 

Create a service account for Default Content Access Account. Register this a/c as Managed Account

Update Default content access account in Search Administration Page. This Account will be used for crawling the content

Add the Crawl Account to the Policy of web applications with Full Read Permissions.

By default, A Local SharePoint sites content source will be created. If you want to add more content sources, you can add more content sources in Content Sources Section

Now Click on content menu of Local SharePoint sites item, select the Crawl options 

Finally if you want move Query Servers and Index Servers to different servers in a farm, You can configure those options in Crawl/Query Topolpgy sections.