Hii Ajit,
You can install Conga Composer directly from AppExchange with your Salesforce Username and password as you install other apps.
If you want to Conga Composer to interact with your data with Salesforce you need to enable security settings.
- To give access conga composer access to user profile you need to enable API Enabled settings.
- If you want to use Salesforce Reports as a data source for Composer then enable “Run Reports” and ‘Export Reports” for the desired user profile.
Hope that will help you out.
Thanks.