What is moderation and certification for access course?

Moderation is where a moderator sent from the exam board goes through a selection of students coursework. They double check that the grades awarded for the coursework is fair and accurate and meet the awarding body's criteria for the grades given.
If they believe the grades are unfair or inaccurate then they can increase our reduce the grades awarded but that rarely happens as tutors normally mark fairly, knowing they can lose the ability to run those courses if they don't otherwise

Thank you for making it more clear to me. Don't mind if I ask some more questions.. When do you think its the best time to start an access course and Should I start mine this week?

The best time is whenever's best for you. I did it at a college so I didn't have a choice.

With regards to how long you have to complete it, as long as you set aside time for your assignments each week you'd easily complete it by the end of May. However, that being said, if you have learning difficulties then you may find it better to have longer to complete it. But it also means that you'd be waiting until September 2022 as nearly all courses at uni only offer September starts. January starts are normally reserved for medical courses such as medicine or nursing

I am currently doing my access course and I only have 3 units to submit, thank god
Do moderators check for plagiarism as well? None of my work has been plagiarised or I haven't been told that I have plagiarised. I am kind of worried about the moderation part because I have 2 borderline distinctions, what if they change, what if i get plagiarised or what if my grades get lowered aghh