Cushy job if I'm to be honest. A lot of staff do like to moan about how the pay is in comparison to TfL etc, but when you compare it with other railway jobs it's not so bad.
CSA duties are divided into different roles. Security is patrolling your area of the station every hour, keeping an eye out for anything unusual i.e. lost property, spillages, access issues. The length of each search varies depending on what station you're working at. Once completed, it's ideal to stand around near the public answering any question or concerns they may have. You also have the option of being first aid trained, so if you take that option, you'd be called on to investigate any reports of an accident/someone feeling unwell. You'd also be involved in some way in the weekly fire alarm test.
Then you have the mobility side of things, which involves assisting passengers in making their journey. Some stations this is handled by TOCs, other stations everything is done by NWR. So this might by guiding a visually impaired person to the train, providing a ramp for a wheelchair passenger, or driving an elderly couple via mobility buggy to the train, if your station has access to buggies. You'd need to be tested to acquire a license to drive one of those buggies, which is fairly easy.
Then you have information, which is as the name suggests. Giving information to customers i.e. directions, train times, journey connections etc. There is also the station 'trade reception' where CSAs often provide cover. Basically signing in visitors/contractors into the station, briefing them on evacuation procedures, reporting any faults found in the station etc.
There is also the option of overtime available which pays decent, so if you fancy a bit more cash you can take up that option. It's available more often than not due to the obscene amount of "sicknesses". Also, unlike other companies, there is no period of time one has to wait before applying for an internal job. So it was common to have people being recruited as CSAs, immediately applying on the internal list and moving on within three/four months. Signalling is usually the common route taken by many. Not that I'm advocating for or against it, just telling it as it is.
Good company to work for that Network rail. There's some bits I may have missed out, but that covers the main bits for CSAs.