To create a web application in SharePoint 2013 follow below steps:
Navigate to SharePoint 2013 Central Administration and then click on Application Management link. This will open the Application Management link as shown in the figure below:
Then click on the Manage web application link and this will open the Manage web applications page and that page you can Click on the New button as shown in the figure below to create a web application.
The above step will open the dialog box to create a new web application. There you should not change anything (But you have option to change) in the dialog box.
Here various options you need to check and also can change according to your requirement like weather you want to create a new IIS web site or not, Name, port number. Virtual directory path (you should avoid to change this) etc.
In the Security Configuration section, you can select weather you want to allow anonymous access or not, Use Secure Sockets Layer (SSL) Yes/No. etc.
In the Claims Authentication type, you can select Enable windows Authentication is you want to enable Claims Authentication.
In the Sign in Page URL section, you can select the Default Sign in Page and also the Public URL.
In the Application Pool section, You can choose for a Create new application pool and give the name of the application pool.
In the Register new managed account section, you can give the User name and Password.
In the Database Name and Authentication section, you can choose the database server, the database name and better to chose Windows authentication.
Now click on OK.
The web application got created.