Help urgent : Web database

I am from designing field...I want to know how to go about doing a web database. I am looking for a job and a friend of mine who has already attended interview told me about the following things asked in the interview.

How r u going to maintain a database of visitors on your database?
How r u going to build a search-engine which gets the information asked by visitors from a central database?
What softwares are best for this purpose and why? [they also asked about what frontend and what backend can go with a linux server...i am not sure about the exact question]
How much time do you take to complete a website with more than 50 pages with complex interlinks?

I am new to this field and these people just want to know if i am aware of the approaches used in web development. they will further give me time to study these concepts and then appoint me. Please help me. I also want to know what are the softwares i need to know..my skills are listed at URL . thanks all.