It used to be easy, especially when they first started online banking. Just enter username and password, and you were in. Now they've made it much harder and I dread it. The banking websites don't always work properly with my computer and browser. I don't want to buy a new computer just because the website has been revamped, and I don't much trust browser updates, so it's often a bit out of date, or my use of ad blockers and NoScript clashes with the new scripts and innovations they keep adding. But I don't want to be tracked or advertised at either. Service providers' websites are even worse for tracking, propaganda and ads, so I don't go there, always use bank transfers.
I also used to dread paying bills when I had to visit the energy companies to pay them in cash, and to write and mail cheques. Can't remember why I hated it. I think I was scared of getting the amount or the address on the envelope wrong, or using the wrong stamp, or turning up at the service provider's shop to find they were closed (I was working in those days and it was hard to find the time to do these things). And I always used to resent paying before the deadline, so I'd wait till that was uncomfortably close. Interest rates were better then, so it paid to wait.