Is there any difference to being paid an hourly rate or an annual salary?

[Mapsandmoremaps]

Hi, I know this may be a very stupid question but I've started a new job and there's alot about the finances I don't understand!

I am on an annual salary but I've noticed that when they create their payroll, it's all based on hours and hourly rates. So, they will list me as 21 hours at £x for the month. Previously I've just been paid based on my annual salary.
I have a contract that states my annual salary and no mention of an hourly rate.

Is there anything I need to be aware of if they're doing it like this or does it just not make any difference?

TIA

If they actually do it on the hourly rate then some months you’d be paid more than others as some will have more working days in than others. Most payslips though will have how many hours and the hourly rate on.