1. What is the use of webtabs? 

https://infallibletechie.com/2013/03/what-is-use-of-web-tab-in-salesforce.html

2. Business process in salesforce?

Lead –> Account, Contact and Opportunity and then Case and Lead.

3. Do we have sales process in Salesforce?

Yes.

4. What is the difference between Default Internal Access and Default External Access?

https://infallibletechie.com/2014/05/external-organization-wide-defaults-in.html

5. Can we able to create the more than one Search Layout?

No