Hey,
What matters most on Access is the quality of your written work. Always remember this, because what happens in-class can intimidate you especially at the beginning, when you're subconsciously comparing yourself to everyone in one way or another. You shouldn't worry too much about in-class participation. This talking over each other and straining at the bit to make an opinion heard - it happened a lot when I did my course, and sometimes there were these overly tangential contributions which dragged on and annoyed a lot of us. It tends to happen when you discuss highly-charged topics such as those covered in Sociology.
That said, the discussions can be useful and are actually part of the whole process. I'd accept that it can be intimidating when other people seem to have a lot more to say on a given topic than you, but remember that it's early days and you're assessed on essays. Also, to state the obvious, everyone has their own style of learning and pace of learning (as you alluded to). Therefore, you might find - as I did - that many things don't make sense during the lesson, but after you sit by yourself and start going over them, processing them, digesting them etc, you begin to 'get it' and it's eureka all the way.
I had a few colleagues who never uttered a word in lessons, and yet wrote impressive essays and earned mostly distinctions. It was always a shock to hear of the grade they earned, because they said absolutely nothing, even when picked on to contribute by the tutors.
I think you'll become more comfortable with it (either contributing or letting others do it) as you attend more lessons.
Best of luck!