Taking a Salesforce exam can be intimidating, and it can be hard to know where to start. I do suggest that you join a local user group because they can help you get started and give you advice on resources. Some of these user groups meetup once a month and other groups meet every week. The community motto is ohana.
For taking the admin exam, I used a few different resources. Certifiedondemand.com is a study guide with quizzes. They have recently updated the material and added in videos. I learned a lot about content and folder management. I also used Udemy. Mike Wheeler has a few courses on different Salesforce certifications. He goes through examples on how to setup Salesforce, create and customize objects and user interface, and automate processes.
I would also recommend taking practice exams. Salesforce does off a practice admin exam for $20. There is also FocusonForce that offers practice exams for $19. You can take a free practice exam to try it out. I have found them very helpful because they include help documentation on all the questions. This allows you to understand the questions that you got wrong. I have found that these tests are the closest to the actual exam.
I created a study guide based off the exam guide that Salesforce provides. I found that it helped to understand what material is covered on the exam. I also created flash cards and had someone quiz me. Here is a link to my flashcards: Salesforce Admin Study Guide.
On the actual admin exam, I found that it was mostly about Vocabulary. Did you know the difference between the automation tools such as would you use a workflow or approval process for the given scenario. Also, there were questions on which chart would I use in a dashboard based off the given scenario. On the exam, some of the questions could have multiple answers. Salesforce does indicate how many answers there are. However, you do not get partial credit for getting two out of three answers correct.
App Builder Exam
For the App Builder, I used Mike Wheeler’s course and FocusonForce again. I also created a study guide and flash cards. Here is the link to the flash cards: Platform App Builder Study Guide. For the exam, I found that you need to have a more in-depth knowledge of the material. For example, if given a scenario, which automation process would you use. Would it be the workflow with a field update or a process builder with a field update. You have to know a little more of the specifics than the admin exam.
I highly recommend that for any exam you wish to take that you set up a dev org and play around in it. Trailhead is a great way to do that. There are hands on challenges and super badges that walk you through a longer process such as how to set up an app. Quizlet is another great resource for any exam. Most of the sets are questions; however, I recommend double checking in the help documentation because sometimes they are wrong.
Finally, I suggest figuring out which resources to use and which strategy works best for you. I used flash cards because I have a good memory and I knew I would retain the material better.
Good Luck on your journey!