Regarding your questions:
1. Have you done any Software testing before? If Yes, please elaborate the job done by you?
Since 2013 I've been doing manual testing (hands on experience in agile frameworks; UI/UX, functional, usability, database and regression testing of web applications).
My job history is available on demand (on my Upwork, Guru and Freelancer profiles).
2. What are the steps involved in a successful App testing?
It depends on the architecture, current stage, volume and priorities of the existing bugs, issues and user stories.
As a newcomer I'll need to learn about the project requirements, development platform, business logic, internal processes and the backlog.
Then I'll need to do an initial exploratory test round and to discuss with the project manager about existing test suits, test cases, or alternatively check lists and test data; automation needs, which modules need attention and what type of testing (functional, GUI, database, user acceptance, API testing etc.).
3. If selected, during which working hours would you be available? And for how many hrs?
My program is flexible, I'm available during 1-2 contiguous time block (1-2 hours each) daily, somewhere in between 9:00 AM and 9:00 PM UTC.
4. If selected, what would be your best per hr rate to start with?
5 USD - this includes my Freelancer fees.