I am new to Salesforce.com and planning to start preparing for Salesforce App Builder Certification. I am learning from Trailhead site and some study material which explains how to create various apps like Warehouse app and Recruitment app. I purchased Mock Papers as well from FocusOnForce.com but still not confident enough to book the exam because of lack of theoretical knowledge. I came accross FocusOnForce Study guide and need to know is it good to buy that material to study properly each topic of this certifiaction? Please suggest how to study fot this certification.
You need to check Platform App Builder Study Guide for the syllabus and start study accordingly.
Try building couple of apps including Recruiting App Force.com Platform Fundamentals which will give you more hands on about the platform.
The study guide also lists Recommended Training and References, you can go through them to gain more knowledge.
Try to understand following topics,
Master-detail relationships, Sharing rules and Org Wide Defaults, Assignment rules, Approval processes, Junction Objects, Workflows, Custom report types, Validation rules, Field level security, Profiles, Record types, Role hierarchy, Relationship rules, Analytic snapshots
Hope this helps. Good Luck :)
Besides using the cert guide as Devendra mentioned, you can algo download the Salesforce University Guide to Certification at https://www.salesforce.com/form/services-training/certification-journey-ebook.jsp
Page 10 has the resources to prepare for the App Builder exam. If you can confidently tackle the seven mentioned trails, and have no problem going through the e-learning I'm pretty sure you can pass the exam.