I am new to scrum , I would be happy if you tell me as a scrum master what should I do in a backlog grooming session and when sprint planning happens exactly and how we estimate the amount of time that we need for each item in the backlog and what planning poker estimates exactly.
It's definitely worth looking at the Scrum Guide for some guidance, though that certainly leaves a lot of room for interpretation. For sprint planning, there are three parts, noted here: https://scrumguides.org/scrum-guide.html#sprint-planning
You're going to want to establish a preliminary sprint goal (the guide notes that it doesn't have to be finalized until the end of planning), then identify which backlog items need to come in to meet that sprint goal, and finally, put together a preliminary plan on how the work will be done. Of course, this is all collaborative. Generally speaking, the PO focuses on the most important work being done first to deliver the most value and the developers focus on what's a reasonable workload and how doing different tasks together may be more effective than others.
Refinement is purposefully vague. It's whatever conversation need to happen to make upcoming Sprint Plannings successful.
Planning poker is a rather broad topic - it is simply a technique for relative estimation. These sizes represent the overall size of an item relative to others. This is not a direct translation to time. Rather, there is a correlation when discussing similar work with a similar team. A great analogy from Mike Cohn is with distance running. A 10k is one size bigger than a 5k, but it doesn't tell us how long a given runner would take and you can't assume that any given runner will take twice as long to run a 10k as they do to run a 5k (or any other clear ratio). However, once someone runs a number of these, you can start making rough time estimates about how long it will take that runner to run similar courses.