Performance Evaluation Tools/Techniques of API in ios

I want to judge how efficient my Api is working at my end to fetch data.How Can I do any code to improve performance of Api at my end?

How Do I judge performance of CoreData to insert, update and delete records?

I am basically not clear with Performance measuring of various controls used at Xcode IDE, So if any thing exist give me a guidance.

Hope You understand my requirement.

Thanks