In this Article, I will guide you how to Promote Domain Controller In the New Forest.
Open Server manager

Select Manage and Click Add Roles and Features,

In Welcome, Click Next

Select Server which you need to promote as Domain Controller

Select Active Directory Domain Services

Select Add Features

Group Policy Management Feature is added by default and no other Features are required, Click Next

It will take some time to get this feature installed. Click on Promote this server to a domain controller

 Select Add a New Forest and add the Domain name, here I have selected windowstechpro.com and set Credentials and Click Next 

Select Add a new forest and Root Domain Name and click Next, Here I am going with First Domain Controller in the New Forest

Select forest and domain function Levels based on your requirement, by default DNS and Global Catalog selected since it is first domain Controller. I have selected Server 20008 R2,

Click next, Since this will be Primary DNS Server,

Click On Next,

It is Recommended to move SYSLOG, Database, and log file to other drive to keep files safe, But I am leaving it as it is,

Review the Settings and click on Next,

Click on Install to promote,

It  will take some time to complete. Please wait for some time

System Will get restarted and after that you can logon using Domain User Account,

You can see active directory Features are added under Tools menu,

Run DCDIAG to review whether domain Controller is installed properly.That is it. You have promoted Domain Controller in the New Forest.