I am doing App Development with salesforce DX module and facing an Error at Build the geolocation app using salesforce CLI, the error given below is flashing. Please help me with that error.

Hi Vruttika, the error indicates that the Salesforce CLI is not detecting a valid DX project in the current directory. 

From your screenshot, the terminal is running from:

D:\Salesforce\geolocation

First, make sure this folder contains sfdx-project.json. You can verify with:

dir sfdx-project.json

If the file is in a different folder, use cd to navigate to that folder and then run the command again.

For example:

cd D:\Salesforce\geolocation
sfdx force:source:push

Also make sure sfdx-project.json is valid and that you're opening the project root folder in VS Code, not a parent or child folder.

If it still gives the same error, please share the contents of sfdx-project.json and the output of dir, so we can check whether the project structure is correct.