can we execute two component in single Salesforce Lightning app ?? If yes, How ??

hi shubham,

yes, we can execute more than one  component in single Lightning App.

<aura:application >
<c:firstComponent />

<c:secondComponent />

<c:ThirdComponent />
</aura:application>

Hi,

There can be any number of lightning component in a lightning app.

An app is a special top-level component whose markup is in a .app resource.
The markup looks similar to HTML and can contain components as well as a set of supported HTML tags. The .appresource is a standalone entry point for the app and enables you to define the overall application layout, style sheets, and global JavaScript includes. It starts with the top-level <aura:application> tag, which contains optional system attributes. These system attributes tell the framework how to configure the app.

System Attribute
Type
Description
access
String
Indicates whether the app can be extended by another app outside of a namespace. Possible values are public (default), and global.
controller
String
The server-side controller class for the app. The format is namespace.myController.
description
String
A brief description of the app.
extends
Component
The app to be extended, if applicable. For example, extends="namespace:yourApp".
extensible
Boolean
Indicates whether the app is extensible by another app. Defaults to false.
implements
String
A comma-separated list of interfaces that the app implements.
template
Component
The name of the template used to bootstrap the loading of the framework and the app. The default value is aura:template. You can customize the template by creating your own component that extends the default template. For example:<aura:component extends="aura:template" ... >
tokens
String
A comma-separated list of tokens bundles for the application. For example, tokens="ns:myAppTokens". Tokens make it easy to ensure that your design is consistent, and even easier to update it as your design evolves. Define the token values once and reuse them throughout your application.
useAppcache
Boolean
Deprecated. Browser vendors have deprecated AppCache, so we followed their lead. Remove the useAppcache attribute in the <aura:application> tag of your standalone apps (.app resources) to avoid cross-browser support issues due to deprecation by browser vendors.If you don’t currently set useAppcache in an <aura:application> tag, you don’t have to do anything because the default value of useAppcache is false.
aura:application also includes a body attribute defined in a <aura:attribute> tag. Attributes usually control the output or behavior of a component, but not the configuration information in system attributes.

Attribute
Type
Description
body
Component[]
The body of the app. In markup, this is everything in the body of the tag.